I too had a 2014 Epic, only replaced her late last year, put many many kms in on that bike. I had a similar issue once, in fact in my first year of owning the bike, but I had been a touch past the recommended full service interval.
Unfortunately it failed the day before the Sani Dragon, so I rode up Sani pass bobbing like a pimps car on the strip, coming down was also interesting.
Sent it in for service, they did the usual swap out at the usual price, issue had nothing to do with the brain, sometimes we think the problem must be with what is different.
I actually like the spez brain shock service practice of swap out. In my experience no matter how buggered the shock is, you always pay the same, and I did at least 7 rear shock services with that bike with them. The cost was also always comparable or less than my fork service.
I did however get a nasty surprise and bill from Rockshox for the fork service once because they had to replace the damper. Spez brain service was also always faster, usually had it back in a week vs two weeks for the fork.
Must admit at first I didn’t like the swap out at all, it just felt wrong, but after doing it multiple times and seeing the benefit I changed my mind on that.