As suggested this 'template' macro is very likely to be the culprit.
To remove e.g. this 'c' > 'o' replacement:
1. Run TSE
2. Load the file which shows the issue with your file extension (e.g. .txt)
3. Execute macro 'Template'
(menu TSE > 'Macro' > 'Execute' > type template > press <Enter>.
you should see nothing happening.
4. Then press <CTRL TAB> to open the template menu
5. That will show you a menu (see screenshot)
6. Select 'List Templates'
7. Now search in the list for e.g. something with
nomen
ncmen
o
c
...
8. When found delete that option by pressing <Del>
and confirming the deletion
9. Otherwise do the same here:
Press <Ctrl Enter> to see *all* templates
and search again.