What is the version of oracle?
SELECT * FROM V$VERSION;
What are the limits set to for PGA_AGGREGATE_TARGET?
show parameter pga;
Past cases with similar messages of
"CAUAJM_E_18402 ORA-04036: PGA memory used by the instance exceeds PGA_AGGREGATE_LIMIT"
were all closed documenting that the dba should be consulted and adjust or disable the limit.
And work with Oracle support if needed.
If they disagree, then the next step would be to provide Oracle AWR reports in 1 hour intervals
from the hours leading up to (when the issue is not happening) and including the problem timeframe (when the issue occurred).
We can then ask our sustaining eng team to review to confirm there is anything additional to consider.