I hope this is proper, but I'm responding to my own post with the solution that worked. I would have added this as a reply to another thread on the topic, but all the ones I found are closed, and don't allow further replies. (For what it's worth, I think that policy decision for the forums is a mistake - for exactly that reason - it discourages people from posting solutions to older issues.)
I ran `dns-sd -B _airplay._tcp` from the command line and saw my list of HomePods, showing their (room) names. I happened to notice that every HomePod Mini that I was having the issue with happened to have an apostrophe in its room's name, like "Bill's bedroom".
Like this:
% dns-sd -B _airplay
Browsing for _airplay._tcp
DATE: ---Sat 24 Aug 2024---
0:15:17.707 ...STARTING...
Timestamp A/R Flags if Domain Service Type Instance Name
0:15:17.708 Add 3 15 local. _airplay._tcp. Kids bathroom homepod mini
0:15:17.708 Add 3 15 local. _airplay._tcp. Bill's bedroom
Then I ran `dns-sd -L "Bill's bedroom" _airplay`, and would get no response. However, if I'd run it on the a homepod mini that didn't have the issue, like the Kids bathroom one (with `dns-sd -L "Kids bathroom homepod mini" _airplay`), I'd get a full/normal response, like this:
% dns-sd -L "Kids bathroom homepod mini" _airplay._tcp
Lookup Kids bathroom homepod mini._airplay._tcp.local
DATE: ---Sat 24 Aug 2024---
0:13:10.644 ...STARTING...
0:13:10.645 Kids\032bathroom\032homepod\032mini._airplay._tcp.local. can be reached at Kids-bathroom-homepod-mini-F434F0131EA8.local.:7000 (interface 15)
acl=0 btaddr=65:6E:F0:31:31:04 deviceid=F4:34:F0:0F:40:9B c=2 fex=AMp/StBLNbwQoQY features=0x4A7FCA00,0xBC354BD0 flags=0x98404 gid=99A44ABF-BBB2-45FF-8516-1623E8EF341A+88A10BAA-28D0-4917-910F-9E61D7B99658 igl=1 gcgl=1 model=AudioAccessory5,1 protovers=1.1 pi=0c9cd339-1a46-4a52-907e-70ccbdbbf399 psi=1C293371-FC40-45D9-A630-30F929EBA141 pk=fbd27d2249d8b862600a647cea1c316db1b250aedf8284da8e5a30906b6c99b9 srcvers=775.3.1 osvers=17.6 vv=1
SOLUTION
In the Home app, I renamed the room from "Bill's bedroom" to "Bills bedroom" - removing the apostrophe. I had the `dns-sd -B _airplay` running when I did this. Everything appeared to update in the Home app immediately, but I didn't see the mDNS airplay entry update until I navigated the Home app BACK, out of the room I had been editing. Then it updated, showing additional command-line output from the already-running `dns-sd -B _airplay` command, like this:
0:17:46.486 Rmv 0 15 local. _airplay._tcp. Bill's bedroom
0:17:59.604 Add 2 15 local. _airplay._tcp. Bills bedroom
Once this happened I was able to further query the newly-renamed airplay destination with `dns-sd -L "Bills bedroom" _airplay` and got the full output as expected. At this point, the original issue of not being able to see timers etc, is FIXED.
Subsequently, I renamed the room back to "Bill's bedroom", adding back the apostrophe. This updated in mDNS as expected, and I haven't seen problems since then.
Note: If you're running these dns-sd commands from Terminal, they don't exit. They print out what they already know, and then sit there, watching for changes or updates. So you can keep them running and watch the changes as they occur. Or, hit Control-C to abort them so you can run some other command.
