If I remember correctly, the "bug" regarding HSRP and STP relates to a "router on a stick" that is also bridging.
If you have a router that is using HSRP and connected to a switch *and* that router is also bridging on that interface, it is possible that the switch will block the port to the router and HSRP/routing will fail.
It doesn't appear to be the problem in your case.
Some notes: using preempt on an HSRP backup interface isn't useful without using "standby track". The priority will never lower on the primary, therefore, preempt is not needed... no harm, but not needed.
If you want to see if HSRP is giving you grief, run a DEBUG STAND and you will see your hellos in and out... also, you will see flapping if its occuring. Also, SHOW STAND will give you good info.
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...