Working sometimes.
WHAT TO ESTABLISH
Is it genuinely intermittent, or consistently different by location or device?
Consistently different by location is usually propagation or conflicting nameservers.
Genuinely intermittent, in the same place, is different.
THE CAUSES OF GENUINE INTERMITTENCY
Conflicting nameservers, where the answer depends on which is asked One nameserver of a pair not responding A resolver problem at your provider IPv6 configured and pointing somewhere that does not work
THE IPV6 CASE
If an AAAA record exists and points somewhere that does not serve your site, IPv6-capable devices fail while others work.
The same device may succeed or fail depending on which protocol it tries.
That produces genuinely puzzling intermittency.
Check whether an AAAA record exists and whether it is correct.
CHECKING NAMESERVER HEALTH
Query each nameserver of the pair individually. Both should answer identically.
WHAT TO SEND US
Times, locations, devices, and whether the failures follow any pattern.
Intermittent problems need evidence rather than description.
