Transient data group failures from iRules

external data groups in 11.4+ are atomic, but there is an issue with internal data groups.

That said, another user had some success with atomic-like updating (for test, ymmv) within tmsh:

while true; do
  tmsh modify ltm data-group internal dg1 records add { /key1 { data data1 }}
  tmsh modify ltm data-group internal dg1 records delete { /key1 } done