I additionally noticed, that closing gtg manually (in opposite to when it's closed by the OS during OS shutdown) and opening it afterwards again *during the same session* keeps the plugins activated (though the above error message is also generated on startup).
When activating the Hamster plugin I get the following error message:
** (gtg:4386): CRITICAL **: atk_object_ set_name: assertion `name != NULL' failed
I additionally noticed, that closing gtg manually (in opposite to when it's closed by the OS during OS shutdown) and opening it afterwards again *during the same session* keeps the plugins activated (though the above error message is also generated on startup).