Cache keeps getting flushed – immediately-changing-to-_index_ssl-html_old/

Per related post – What I have done to overcome this problem:

1.
/wp-content/plugins/w3-total-cache/PgCache_Flush.php
public function flush() {
if ( $this->debug_purge ) {
Util_Debug::log_purge( ‘pagecache’, ‘flush_all’ );
}
//comment out this line: $this->flush_all_operation_requested = true;`

2.
/wp-content/plugins/w3-total-cache/Cli.php
function pgcache_cleanup() {
$this->flush_all_operation_requested = true; // add this line

Hello @onewordpresscustomer

Thank you for reaching out.
_old files are created when the cache is purged.
It’s fine to have _old files. If you always have only _old files – that’s a sign something purges cache all the time. Like theme or some plugin.
The solution that works for you prevents that something outside of W3TC calls for the cache to be purged.
I hope this helps!
Thanks!

Hi Marco – just wanted to provide an update of my findings on this case.

1) I reverted the changes above – as that seemed to also cause inconsistencies when I try to manually purge the cache from the Admin console – so I reverted back to a normal installation which re-introduced the same behaviour.

2) I have identified the scenario that caused the ‘Flush All’ issue as follows:
2a) The issue only occurs when I have the YOAST SEO Plugin activated. With Yoast de-activated it does not occur.
2b) The issue also only occurs when I cache a specific page – in my case the contact-us page. Everytime this page gets cached – it triggers a ‘Flush All’ at the end and leaves all pages on the site uncashed (_old) again.

3. I tried updating the page (it was a very old one), changing the url (slug) and re-publishing, but the error persisted.

4. To correct the issue, I created a new contact page and swapped out the url.

I can’t figure out why this would only occur with Yoast activated as the ‘flush all’ normally only (normally) happens with a Yoast initial activation or de-activation.

Anyhow – Cache is looking normal – so far so good.

Hello @onewordpresscustomer

Thank you for the information.
Glad to know you found the source of the issue and managed to fix this.
A similar problem was occurring with the RankMath plugin.
Let me know if the issue starts to re-occur.
Thanks!

Short Update – I had a similar issue since with one of the sites product tag pages (a bit easier to find now). After re-creating the tag from scratch (and testing all the other tags on the site) all is now running well after 24 hrs.

For info: From the logs the flush happens after a call by ‘ao_speedup_cachebuster’ i.e.:
[Fri, 06 Aug 2021 12:00:30 +0000] [/wp/?ao_speedup_cachebuster=71254] [https://sitename/wp/?ao_speedup_cachebuster=71254] flush all
[Fri, 06 Aug 2021 12:00:31 +0000] [/product-tag/tagname] [-] storing cached page: true original true reason
[Fri, 06 Aug 2021 12:00:31 +0000] [sitename/] [-] flush all

My theory is that Autoptimize ran into some issue with caching this tag and this in turn triggered a flush event.