Unable to edit themes with this plugin installed

Custom Contact Forms Version 7.8.5
WordPress 5.0.3

I have been getting an error when trying to edit themes “Unable to communicate back with site to check for fatal errors, so the PHP change was reverted. You will need to upload your PHP file change by some other means, such as by using SFTP.”

Disabling this plugin makes the error go away and it becomes possible to edit and save themes.

The only clue I have comes from here:
https://www.ads-software.com/support/topic/cant-edit-main-theme-php-files-after-upgrading-to-4-9/page/8/#post-9718186
which says:
“the issue is with plugins that use PHP Sessions. After the session_start() command, php session hangs causing a timeout. This prevents the loopback request. I found out that when the session is closed with a session_write_close() command, the issue disappears, and everything is working fine again. So the real issue does not seem to be on the php session itself, but rather to the open php sessions that never close. I guess that the open session locks the session files in php (?) and creating the problem.”

• This topic was modified 5 years, 9 months ago by NoNewWars. Reason: Typo