I don't know what could cause that. There is nothing in ReReplacer that directly calls that class.
Can you give me (super) admin and (s)ftp access so I can take a look?
And tell me on what url I can see/reproduce the issue.
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I think the is something wrong with the replacer installation on my staging site. Maybe as cause of the upgrade to j4 on the j3 site everything is alright.
So if you have a look at the screeshots you see two component entries 'ReReplacer' und 'Conditions' looks like a duplicated entry?!
Do you have an idea how this could happened and hat is the way to solve this.
I have no idea what change could account for that error. Not that much has been altered.
Anyway, I can't/won't use a Joomla file browser to change files. If I change something that breaks the admin, I have no way to fix it.
So if you can provide direct (s)ftp access, I am happy to look into this further.