Expression Engine Control Panel Timeout issues - is there a solution?

I have been having an ongoing issue is that the control panel times out - often in the middle of updating entries. I have to log in again and all edits have been lost. I am hoping that I can get a final resolution to this issue so it never happens again.

The problematic site is running EE 3.5.17.

I have the config file set with the following:

$config[‘require_ip_for_login’] = ‘n’; $config[‘require_ip_for_posting’] = ‘n’; $config[‘cp_session_ttl’] = 86400; $config[‘user_session_ttl’] = 86400; $config[‘admin_session_type’] = ‘c’;

These settings notwithstanding, sessions may last 15-30 minutes max with no predictable timeout.

If there are not any more reliable settings that work for EE 3.x will upgrading to EE 4 solve the problem. I have been slow to update this site because of module dependancies.

I would really appreciate some wise insights on solving this issue.