It has happened to me many times not to be able to use the "Find and Replace" tool on ETS6, it gives me the following error:
"An internal error occurred.
Value cannot be null.
Parameter name: value"
It seems to me that this usually happens when I have more than one tab open, that is, 90% of the time I can't use this tool.
I have also had some issues where the ETS6 freezes and has already been reported in other posts.
Another problem that sometimes happens to me is that sometimes the program doesn't seem to associate the Group Addresses in the right place, I can't always replicate the problem, so I can't give more details about this issue.