Disconnected and Connection Failed

I have 915mHz radio telemetry.
Although there is no problem in the first connection to each other, the connection is constantly disconnected and it takes a long time to reconnect.
The disconnection is not at a long distance, but also when it is side by side. Is there any special setting I can do about it?

It is never a good idea to operate a transmitter without an antenna. Low power devices might survive, higher power transmitters will be damaged.
So I hope, you only removed the antennas for the photo.

Yes of course, I don’t use it without antenna.
Frankly, I’m not sure how many mw my telemetry is.
But my biggest problem right now is disconnection and hard to reconnect.
I set the TX power to 20 and it disconnect, I set it to 17 and it breaks again…