Alright, that could theoretically explain these issues.
The thing is that the VTP Pruning sometimes likes to declare all VLANs pruned on a trunk. VTP Pruning functionality is provided by switches sending VTP Join messages every 6 seconds, and each Join message contains a list of used/unused VLANs as seen by the sending switch. The funny thing is that if the VTP Join messages have been arriving on a trunk port and suddenly stop arriving, the receiving switch declares all VLANs as unused and prunes them off the trunk.
This can be very unpleasant if, for example, you migrate a VTP Server/Client switch to a VTP Transparent switch: it will stop originating VTP Join messages and in 6 seconds or so, all surrounding switches will prune all VLANs on their trunks to this switch. I am wondering if some situation like this took place in your network - that without an interface flap, some VTP Joins stopped arriving.
Nothing really happened like that. We only replaced (reloaded) our HSRP secondary core switch. The IDF that was having trouble was always vtp transparent. We've done this several times in the past (at multiple sites) and it only seems to happen at this site. The real problem is that I can't replicate it in the lab. I have all the same equipment, IOS, configs, etc and can't make it happen.
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...