It's almost certainly to do with your particular third party plugins. That is why nobody else is reporting it.........
I had a hard time figuring out which plugins caused that error.
One by One, Try and Error, and i had 4 of them causing the problem.
C2 does not give any indication about what plugin is the problem.
They had in common that they are old (probably forgotten), also they all are 'faceless'.
Of course it is not happening with a fresh install. Do you really want me to find & download & install all 3th party plugins again ?
On the good side, none of Rexrainbow plugins are a problem, none of BackendFreak's plugins have a problem. And is why i did not report it, it was a good thing after all, cleaning my plugin mess.