what about V$ARCHIVE_GAP?

That might help. Also consider that FAL does work so that view
may give you false alarms

for instance

log 1 shippied and applied to standby
log 2 starts to ship and network hiccups, log does not get sent
when log 3 is generated it will detect the gap and send log 3 and log two

In that instance it's possible that log three gets received first and hence a gap may be detected.