The exact same issue happened to me, it cleared up after 2 days by its self! As I'm still having high latency to wherever i ping for each machine behind this FTDv
Just ran the capture trace and see some sort of connection limit is being reached. I have a single VM using this internet connection right now.
Drop-reason: (rm-conn-limit) RM connection limit reached
It would appear we are being slammed from the outside.
firepower# sho conn count
95596 in use, 100001 most used