The below issue was caused by a change in domain controller for the Portal's IWA identity store config.
"Wal files size exceeded the maximum size"
These errors occur in the portal logs every minute and began to occur at the same timestamp as the IWA config change. No other change occured on the Portal machine at this time.
Despite these errors, the ArcGIS Enterprise (10.6) is functioning as normal and the underlying postgres db seems to be behaving fine. The walarchive is consistently increasing as per the 60 minute archive setting in postgresql.conf. These archive dumps are all 16,384 KB and have modified dates AFTER the above change and errors began to occur.
Therefore, I do not believe anyting is actually going wrong and impacting users, but there is clearly a config/setting somewhere which is tied to the old domain controller. Any thoughts as to where I can investigate further? The underlying postgres logs indicate no issues in this space.
FYI, we do not use webgis DR and do not plan on using this as a solution moving forward due to the scale of our deployment (some incremental backups took 7+ hours to complete).