I have the same problem. I’ve been getting invalid Shriekwing logs for a couple of months now. Only Shriekwing and only recently. All other encounters are fine, including M+.
I recently moved house and got a new computer, and it’s still happening. Which suggests that either it’s the Warcraft logs app, or it’s something to do with our config or addons. Since it looks like the problem is pretty rare, I suspect it’s an addon that is doing it.
It looks like the fight goes until about line 18788, at least events are still occurring at that point, but the counter is reported as having ended at line 18515 and the unit died at 18519. The encounter started on line 104.
It looks to me like the encounter started at 7:43pm and ended at 7:46pm. About 3 minutes and 30 seconds all up.
But the log says the fight went for 1 minute and 15 seconds.
I do live-logging and DBM takes care of enabling combat logging on the pull timer. It’s same as what I’ve always done.