I think what slim was getting at is the WHMCS Domain Synchronisation Cron Report is showing domains being updated to the same dates. I have mine set for 4 hourly emails and I get the same list every 4 hours with the same domains changed to the same dates.
I have: Tick this box to enable automated domain syncing with supported registrars via cron, Enable - Number of Days to Set Due Date in Advance of Expiry, both ticked with 14 days sync.
I used to just get all the domains were synced, now I get they change to the same date every email:
REDACTED: Expiry Date updated to 30/09/2021, Next Due Date updated to 16/09/2021
Then 4 hours later, same domain:
REDACTED: Expiry Date updated to 30/09/2021, Next Due Date updated to 16/09/2021
I've obv removed the actual domain but thats just 1 line of the report. Every domains changed, yet the dates shown in WHMCS match the dates their changing to. Kinda odd.
Hope that explains better what we see.