Trust this computer errors

I have read all the docs on errors with 'Trust the Computer' messages on the iphone - but can't find anything that talks to the underlying problem.

When I connect my iPhone Xs Max to my new 16" Macbook Pro I get the message 'Trust this computer'... once I accept this functions like USB hotspot works.

However, I keep getting problems where the iPhone forgets that it knows this computer... and then asks for permission again. When it gets into this mode it doesn't matter how many times I say 'Trust this computer' and enter the code... the computer does not see the iPhone and things like "iPhone USB" hotspot do not work.

When it gets into this mode the only way to fix it is to "Reset Location & Privacy" settings on the iPhone - then it forgets whatever has it stuck in this 'Trust this computer' loop.

I am not 100% sure what triggers the problem but I think it might have something to do with using VPN... it looks like when I activate VPN (via ExpressVPN) it causes this problem.

Looks a VPN bug on the iPhone that is causing the trust settings to get corrupted.

Is this a known bug and is there a way to fix it?

Both the Macbook and iPhone are on the latest software.