Funcom added a purge meter decrease when players are offline multiple days. This was to try and get purges to activate on current active clans instead of triggering on inactive clans in the server database which had full purge meters but no buildings left on the server to target.
I think they have made this decrease too steep as you only need to be offline for 48 hours and the progress is massively decreased.
For example if you have increased the meter by 5% through a few hours play … log off for two days … come back and that progress is wiped.