Background
Running Stellarmate OS 1.7.9 on my own Rasp Pi 4B 8GB, OS is on a USB 3.0 connected SSD (blazingly fast!!).
All astronomy functions are working well.
Running my rig in the garden with the Rasp Pi attached to the side of the mount and set up as a hotspot.
Kstars / EKOS and PHD2 software is all running locally on the Pi and I am connecting via RealVNC with a PC that is less than 10 meters from the rig, through one pane of glass.
The Rasp Pi is facing the window with direct line of sight, it is never being blocked by the mount as it moves.
Stellarmate is running as a hotspot. I had read that USB 3.0 and the 2.4GHz band can sometimes have issues when in close proximity, so I set the hotspot to transmit on 5GHz.
Ambient temperatures are between 0 and 5 degC.

Problem
Sessions start out okay, but after about 2 hours, the connection gets "flakey" over a period of 5 to 10 minutes then dies completely.
Hotspot wifi signal seems to be unreliable.

Symptoms
After loss of connection, if I check the hotspot signal from my PC, it looks strong, but RealVNC cannot re-connect.
On a couple of occasions my PC loses the hotspot wifi signal and gets kicked off, but the hotspot is still showing as transmitting with normal power.
While not connected to the hotspot, the PC is reporting a strong signal, but as soon as it connects, the signal strength apparently dies completely. Once the PC is disconnected, the signal is showing as strong again.
Tested with a second PC and even a Smart Phone and get the same display of signal strength as explained above.
Took my notebook outside just 1 meter from the Rasp Pi, and still no connection.
Final solution has been to go out to the mount, physically reboot the Rasp Pi and restart the session, which then continues normally for another 1-2 hours before repeating the same issue.
Happened 3 times last night before I called it quits for the evening.

Would there be any advantage is installing an external USB wifi dongle?

If there are any logs I need to record and post here, or if there are any ideas, I'd appreciate some feedback

Rpi wifi is known to be weak unless you are sitting alongside with your computer. I think most people at some point decide to use an ethernet cable or ,alternatively, arrange for a strong outdoor house wifi.

Thanks for responding, but I think it is more than weak signal.

As I mentioned, I can take my PC to within 1 meter and get no response. I even tried to connect by Direct Ethernet (I have it set up to allow), but there was no response from the Pi. If I had to guess, I'd say it was some software issue that is causing a lockup or crash, but as I can't connect into the Pi as it is happening, I am unable to diagnose.

Running htop shows any significant system load?