HA accessibility on home network

I am abbreviating this otherwise it will end up way too long (as I’ve put many hours effort into this already) and put people off!! I hope it makes sense.

8Gb RPi 4 running HA on SSD, hardwired to LAN. No WiFi. Pi Processor is in the low single % most of the time. Disk use is < 20%. Memory is about 20%.

Google Home speakers which are connected wirelessly thru TP-Link Deco mesh regularly but randomly have trouble accessing it - “can’t find HA”. This can happen for a while then suddenly works OK for a while with me changing nothing. I am using DuckDNS and have been working on getting local fulfilment but each time I hit one stumbling block or another when my playtime runs out and have to revert.

So I also less frequently get Unable to contact HA on my phone from the Companion app. It sometimes takes two or three ties to get through. Related to the problem above? I’ve no idea but I’ll put it out there in case anyone has any ideas.

I never have connectivity problems on my hardwired PC.

Pinging the Pi from the PC is consistently very fast (hard wired to hard wired). Pinging the Google device from the PC (hard wired to WiFi) is not quite as quick but no significant lags. Pinging the Google device from a PC on the WiFi is the same. I don’t believe I have any local network problems. I’ve changed the CAT5E (router to Pi) just in case it’s that - it isn’t.

So what can it be? Which logs would be useful to look at? What other tests can I do? Is it worth restarting with a new HA image (though the backup restore would overwrite wouldn’t it?). I’m a bit stuck with what to try next, except get the local fulfilment going - which won’t help my phone.

NB I did wonder if the disk was dozing off and taking a while to get going again (i.e. longer than the app timeouts) - but it’s an SSD and if that were the case the first call might fail but likely the second would be OK.

FWIW the latest HA update seems to have so far eradicated the Google Home
problem. Early days though

EDIT: Ignore that, today it doesn’t work reliably again