Just to test regex in black function list, I made these changes (kept regex only in black function list)
>'[A-Za-z]*currval' and 'currval' will both match
table.table_seq.currval might not match with 'currval' only, we need regex for that. Still, you can test these both.
> Again, we are finding that load balancing works but under load we are seeing nextval being sent to the standby
There must be some SQLs which causing issue and these are hitting under load only. Try to find out these SQLs and test these without load.