Thanks for letting us know. This has been already discovered with mono 4.2.1 running on mac os x, identified as affecting only this platform... The workaround implemented and released last week works, but it wasn't included in Linux release. It will have to wait for the next PicoScope release round I'm afraid (possibly Feb/March next year)
In mean time I advise to not use version advertised on mono-download website (4.2.1 / 4.3.0) and stick to system provided ones (most ubuntu clones will use 3.2.8 ).
Another thing to try in this case is to compile older version yourself and install it under different location. Then change /opt/picoscope/bin/picoscope script to use that version - modify MONOCMD variable acquisition to fixed value with new location in it.
I confirm building mono 3.12.1 and gtk-sharp 2.12.29 solves the issue and picoscope application works just fine. I'm on Arch Linux (where the default system-wide mono package is at version 4.2.2).
There is no need to downgrade the system packages: just configure, build and install the above two packages with another prefix (i.e. /opt/picoenv). Also don't forget to modify the official picoscope shell script: MONO_CMD=/opt/picoenv/bin/mono.
This way the system will continue to use the default system-wide mono and gtk-sharp packages, while picoscope will use the custom built ones.