Pulling this thread out of the 7.5 release thread incase others run into the problem.
References from 7.5 release thread:
http://forum.mikrotik.com/t/v7-5-stable-is-released/160518/1
http://forum.mikrotik.com/t/v7-5-stable-is-released/160518/1
After applying 7.5 on a CCR2116, a large percentage of packet drops occur on source natted flows. Non natted flows are unaffected and seem fine.
Starting Torch, disabling l3 hw offload, or reverting to 7.4.1 appear to correct the behavior. I opened a support case as a result: SUP-91363 if anyone needs a reference.
Update 1:
Further testing in a lab CCR2116 where I can control routing more accurately. The issue is reproducible with source nat with masquerade configured. In a lab environment where I can turn NAT on/off without changing flow of traffic routing wise. I found after a short period of time of nat rule enabled, the issue will occur. Seems to affect all traffic that is offloaded and source nat, regardless of protocol. Traffic that is offloaded but not source nat has no loss which I can confirm by disabling nat firewall rule close existing connections, packet loss disappears for new connections. If i close connections again, and re-enable nat rule, packet loss is back. - All of this done w/o disable l3hw offload on switch config.