# How to fix an unresponsive simulation with red square dots in top-left corner **URL:** \ **Category:** Knowledgebase\ **Created:** [November 18, 2025, 9:28am UTC](https://get-help.theconstruct.ai/t/how-to-fix-an-unresponsive-simulation-with-red-square-dots-in-top-left-corner/38962 "2025-11-18T09:28:11Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![bayodesegun](https://get-help.theconstruct.ai/user_avatar/get-help.theconstruct.ai/bayodesegun/32/10684_2.png) [@bayodesegun](https://get-help.theconstruct.ai/u/bayodesegun)\ **Post date:** [November 18, 2025, 9:28am UTC](https://get-help.theconstruct.ai/t/how-to-fix-an-unresponsive-simulation-with-red-square-dots-in-top-left-corner/38962/1 "2025-11-18T09:28:11Z")
![Screenshot 2025-11-17 041359](https://get-help.theconstruct.ai/uploads/default/original/2X/3/307ce1b9311025b98a3b0e7f92b88d565898e702.jpeg) When you notice that there are red square dots on the simulation window, in the top-left corner, as shown in the image above, please try the following: ### 1. Check the use of VPNs, proxies, and firewalls - Are you using a VPN? - Are you behind a firewall or web proxy - Check your Internet security software (if any) Any of these could interfere with the connection to the simulation services. ### 2. Trying a different browser To better understand what is happening, could you use another Web Browser to see if the same problem occurs? If you are using **Microsoft Edge** , for example, could you try loading the course using **Mozilla Firefox**? If Firefox doesn’t work, could you also try it with **Google Chrome**? As you can see, on the top left side of the simulation, we have a small **red square**. If it is red, then the robot will definitely not move. When trying different browsers, the goal is to see if that square becomes **green**. The reason we ask you to try different Web Browsers is to see if there is an add-on/extension in your browser that may be causing the issue. ### 3. Trying a different network As a last resort, if after trying all web browsers it still doesn’t become green, **could you also try a different network** to ensure there is not a firewall blocking something? If you are trying from home, for example, could you try from your university or work, or vice versa? ---
**Author:** ![ci3m](https://get-help.theconstruct.ai/letter_avatar_proxy/v4/letter/c/85e7bf/32.png) [@ci3m](https://get-help.theconstruct.ai/u/ci3m)\ **Post date:** [November 19, 2025, 11:10am UTC](https://get-help.theconstruct.ai/t/how-to-fix-an-unresponsive-simulation-with-red-square-dots-in-top-left-corner/38962/2 "2025-11-19T11:10:37Z")
Hi, We are experiencing the same issue now, and it’s quite chaotic. It appears that it might be related to the web browser. In Firefox, disabling Firefox Protection and all add-ons, as well as clearing the cache, has worked. We are still investigating the issue, but we would appreciate any insight from your side. Best regards, ---
**Author:** ![rtellez](https://get-help.theconstruct.ai/user_avatar/get-help.theconstruct.ai/rtellez/32/9813_2.png) [@rtellez](https://get-help.theconstruct.ai/u/rtellez)\ **Post date:** [November 19, 2025, 11:26am UTC](https://get-help.theconstruct.ai/t/how-to-fix-an-unresponsive-simulation-with-red-square-dots-in-top-left-corner/38962/3 "2025-11-19T11:26:26Z")
For which course are you experiencing the problems? ---
**Author:** ![ci3m](https://get-help.theconstruct.ai/letter_avatar_proxy/v4/letter/c/85e7bf/32.png) [@ci3m](https://get-help.theconstruct.ai/u/ci3m)\ **Post date:** [November 19, 2025, 11:28am UTC](https://get-help.theconstruct.ai/t/how-to-fix-an-unresponsive-simulation-with-red-square-dots-in-top-left-corner/38962/4 "2025-11-19T11:28:51Z")
ROS2 in 5 days (Python) ---
**Author:** ![ci3m](https://get-help.theconstruct.ai/letter_avatar_proxy/v4/letter/c/85e7bf/32.png) [@ci3m](https://get-help.theconstruct.ai/u/ci3m)\ **Post date:** [November 19, 2025, 11:39am UTC](https://get-help.theconstruct.ai/t/how-to-fix-an-unresponsive-simulation-with-red-square-dots-in-top-left-corner/38962/5 "2025-11-19T11:39:17Z")
On the university network, none of the navigators are working. I’ve tried the new and old interface. On Firefox console I’ve got this error: WebRTC: ICE failed, your TURN server appears to be broken, see about:webrtc for more details ⛔ Dropped:ICE connection dropped: 4 [index.js:459:16](https://app.theconstruct.ai/godot-ipad/mars_rover/v2025.05.12/web_export/index.js) 🔁 WS closed — reconnecting… [index.js:459:16](https://app.theconstruct.ai/godot-ipad/mars_rover/v2025.05.12/web_export/index.js) 🔁 WS closed & DC not open — reconnecting… [index.js:459:16](https://app.theconstruct.ai/godot-ipad/mars_rover/v2025.05.12/web_export/index.js) ⛔ Dropped:ICE connection dropped: 5 [index.js:459:16](https://app.theconstruct.ai/godot-ipad/mars_rover/v2025.05.12/web_export/index.js) 🔁 WS closed & DC not open — reconnecting… 89 [index.js:459:16](https://app.theconstruct.ai/godot-ipad/mars_rover/v2025.05.12/web_export/index.js) 🔁 Attempting quick reconnect… ----- edit the error with more message — Firefox ne peut établir de connexion avec le serveur à l’adresse wss://i-06f31e44c6913f792.robotigniteacademy.com/4c70db7b-f0eb-4eda-97d1-bff46fd71019/websocket/12005/. ---
**Author:** ![bayodesegun](https://get-help.theconstruct.ai/user_avatar/get-help.theconstruct.ai/bayodesegun/32/10684_2.png) [@bayodesegun](https://get-help.theconstruct.ai/u/bayodesegun)\ **Post date:** [November 19, 2025, 3:22pm UTC](https://get-help.theconstruct.ai/t/how-to-fix-an-unresponsive-simulation-with-red-square-dots-in-top-left-corner/38962/6 "2025-11-19T15:22:34Z")
I’m sorry that you are experiencing this issue. - Please let us know the exact unit of the course so we can troubleshoot the specific simulation. - Also, it appears the university network is blocking WebRTC data (UDP port 3478). - Have you loaded the simulation successfully before now? If so, did you change something recently? - You mentioned earlier that Firefox worked after taking some actions - was that on the university network or elsewhere? - In the unlikely event that there was a problem with your VM, this should reset the next time you come back… ---
**Author:** ![rtellez](https://get-help.theconstruct.ai/user_avatar/get-help.theconstruct.ai/rtellez/32/9813_2.png) [@rtellez](https://get-help.theconstruct.ai/u/rtellez)\ **Post date:** [November 20, 2025, 8:51am UTC](https://get-help.theconstruct.ai/t/how-to-fix-an-unresponsive-simulation-with-red-square-dots-in-top-left-corner/38962/7 "2025-11-20T08:51:18Z")
Hi Clement, I answered you privately by email ---
**Author:** ![bayodesegun](https://get-help.theconstruct.ai/user_avatar/get-help.theconstruct.ai/bayodesegun/32/10684_2.png) [@bayodesegun](https://get-help.theconstruct.ai/u/bayodesegun)\ **Post date:** [December 31, 2025, 10:06am UTC](https://get-help.theconstruct.ai/t/how-to-fix-an-unresponsive-simulation-with-red-square-dots-in-top-left-corner/38962/8 "2025-12-31T10:06:34Z")
A post was merged into an existing topic: [Python for Robotics course Bug - Cooper error](https://get-help.theconstruct.ai/t/python-for-robotics-course-bug-cooper-error/39412/9)