I upgraded from an old Apple SE to an iPhone 13 Pro running IOS 15.3.1.
My Series 5 Apple Watch was running the latest software Watch OS 8.4.2.
After the upgrade the watch was unusable because there was a several second lag in speech. Looked around and tried a couple of things and after 2 days I called Apple Accessibility Support.
This is what we found:
On the watch went to:
Apps/Settings/Siri/SiriVoice and it said “Waiting To Download” so went to
Settings/Wi-Fi and the watch was not connected to a network. Underneath it said choose a network and we didn’t find our networks in the network list.
We rebooted our home router which has 2 networks. When we tried to connect the watch to a network it would not connect. Went to the iPhone and attached the iPhone to the network we wanted the watch on. The watch automatically connect and after putting the watch on the charger it started downloading. After the download completed the watch worked. We had to go through the Siri voice set up.
Hope this helps someone else. The solution was sooo simple after the fact.
I had something like that happen on my Watch SE when I got my 13pm. I ended up doing a factory reset and restoring from the latest backup which fixed the problem as well.