That's strange - I don't see that problem. Although that code was touched in recent commits. Could you try regenerating your visual studio project? Also you could try the daily build of H16 (16.0.689) to verify that the problem is with your own build or not.
I regenerated the VS project, deleted Binaries/Win64 and Plugins/HoudiniEngine/Binaries/Win64 and restarted Unreal which rebuilt the source. No change to the toggle button issue.
I am already using 16.0.689 with an up-to-date checkout of the HoudiniEngine plugin source.