Well, I thought 19.07 rc2 was stable on my EA8500's, but when I configured one the same as the EA6350v3 that 19.07 rc2 was crashing (i.e., replaced EA6350v3 with EA8500) for my first floor AP, I'm seeing the same problems - only difference is the EA8500 has 512MB of memory to hide the problem better.
A spike in CPU usage (core 1 jumps to 1.4 GHZ and 100% usage) occurs just before the memory use starts slowly climbing up from a too high (for the light load) ~150MB to ~210 MB, then drops to ~180 MB. This unit is only being used as an AP for two SSID's each on 2.4 and 5G (a main and a guest each) with a couple wired clients plugged into the ports. I'm using the ath10k-ct, but as noted previously, swapping to the non ct didn't help on the EA6350v3.
And as I type, wifi on the second floor EA8500 running 19.07 rc2 just crapped out too. Which is odd, because it had been fine for days. I changed one thing - I added the cpu frequency plugin for collectd. Guess I'll not be installing that again anytime soon.