'Session Expired' when trying to save functions.php file

Operating System & Version
CentOS v7.9.2009 [server] v100.0.1
cPanel & WHM Version
CentOS v7.9.2009 [server] v100.0.1

sayleboat

Registered
Oct 31, 2021
2
0
1
Richmond Hill, Georgia
cPanel Access Level
Website Owner
For some reason, any time I add PHP code to my functions.php file - when I click 'save', it tells me my session has expired.

If I add a comment, or regular HTML - I can save it just fine. However, I can't add or remove any <?php code

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