I'm sorry to hear that you're experiencing issues!
I've tested your setup and I cannot recreate this issue. I was using RUT9_R_00.07.03.2, could you try updating to this version(ideally without keeping settings)?
If that does not help, I'd like you to recreate the issue (Turn off the WiFi WAN router, turn it back on and wait a few minutes) and navigate to System → Administration → Troubleshoot. The file can be attached to the original post and will only be visible to Teltonika moderators.
I'd also like to ask you to test if the same behavior occurs when connecting to your phone hotspot or any other router.