What is causing RST ACK in my connections?

75% of calls to a 3rd party API are getting dropped.

Here is a wireshark capture of RST ACK happening with 2 calls: Failing Capture.

Here is a wireshark capture of a successful connection for comparison: Success Capture.

I cant figure out what is causing the RST ACK flag. Couple things I've noticed. TCP DUP ACK is common between both success and failure. It seems to recover from it sometimes. The Server doesn't seem to support SACK_PERM=1. Not sure if that is relevant or not.

Any ideas on why a TCP RST ACK is happening?