Forgot to say, the steps used fails in the same way every time
Thank you very much for your feedback. I can see in the log that it works the first time then once you restart the plug-in editor, it doesn’t work anymore, the polygon never manages to be created (exactly like in the video). I’ll try to retrace the way that leads to this. Maybe I will send you another version with more logs. Sorry for the inconvenience and thanks again for the feedback!
Again I downloaded another version, ASAP-v1.3.0-dev3b-Linux. If you could clean up the logs folder, do the same test, and send me the new log files back, that would be great 
!
Moreover, the log pointed out to me that on your system the plug-in cannot check the new version and that certain actions are executed on the wrong thread. I’ll sort this out later but I should probably ask you for new tests, sorry 
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After being recreated, the plug-in editor loses keyboard focus after each mouse click. This shouldn’t happen, because losing focus resets the current action, which is why you can’t have more than one point. I need to find the cause of this problem, but it’s possible that it’s independent of the plug-in and is a bug in the focus management. Once I’ve found out exactly what’s going on, I’ll try to find a fix or forward the detailed problem (to the Reaper team if the problem comes from their side, for example). I’ll probably ask you for some more tests, sorry for the inconvenience.
I see. If i keep clicking ‘randomly’ - some very few times (1/100?) a polygon (triangle) appears, only to disappear upon the next click. Haven’t been able to distille any pattern.
For the sake of it I tried now changing my preferred ‘hover’ behavior in my window-manager, from ‘hover-window-to-focus’ to ‘click-window-to-focus’, without any change in the polygon-tool.
Yes, please ask for more tests. I’d be very happy to help!
I’ve uploaded version 1.3.0-dev4 which contains the ARA plugins in a standalone application version. For various reasons, the Spectral Surface plug-in has been renamed Psycho Filter, so if you can test the Psycho Filter application 
If you can test it, it would help to understand where the problem comes from.
Good news, if you can do a 
it’s a good sign and at least you have an alternative. On the other hand, the problem surely lies with Reaper, so I’ll pass the information on to them. If you have any other feedback or suggestions, don’t hesitate!
Great work. Pls. ask if you need some special-case-debugging-stack-tracing of any sort, short of replacing my OS