Hello,
Thank you for contacting Teltonika Crowd support community.
I would like you to check if the antenna connectors are screwed properly.
Depending on the environment and surrounding objects, try changing the placement of the router.
Check your configuration by following this video.
Also, login to the WebUI and navigate to Network -> Wireless. Edit the global wireless device settings and in a General setup tab try setting channel width to 40MHz. More details here. You can try different channels if you are in an area with more wireless devices around.
Kind regards,
Shadrack