Strange... I did not change a single byte of the copy/paste code for macOS in like... years !
I do not see why there would be any difference between the two versions you cite, unless something changed on the compilation step side. Catten would be able to reply to this question...
In your log, I also see that the viewer crashes on exit in the keyboard handler... Is the previous version producing the same log (i.e. does it crash on exit too) ?
EDIT: the (years old) change that is causing this is a workaround implemented to avoid seeing a 'nul' character appended to the pasted text on macOS. Somehow, this bug won't happen any more with v1.28.2.56 (compiled with a new Xcode version ?) and so the workaround needs to be changed as follow (in linden/indra/llwindow/llwindowmacosx.cpp):
I.e. instead of unconditionally removing the character, we must now test and see if it indeed is a 'nul' (the added "&& dst[len - 1] == '\0'" test).