BT Homehub 5A 19.07.7 crashes

Hi All,
I've been using a BT Homehub 5a with older (Lucy) firmware for ages, and it was incredibly reliable - except it failed if I had too many static DNS entries.
ISP is UK Plusnet via Openreach FTTC.
So I took a 2nd hub and upgraded to 19.07.7 (stock, no mods).
This version copes with the increased number of static DNS entries (i.e. does not die when I add them, like the older version), but is up and down like a yo-yo. I'd say uptime is < 1 day. Previously it never rebooted and I never noticed loss of DSL.

Questions:
1/ I did see somewhere someone mention a different firmware for the DSL? - i have these in my log:

[   11.108141] Lantiq (VRX) DSL CPE MEI driver, version 1.5.17.6, (c) 2007-2015 Lantiq Beteiligungs-GmbH & Co. KG
[   11.120758] Lantiq CPE API Driver version: DSL CPE API V4.17.18.6
[   11.180548] Infineon Technologies DEU driver version 2.0.0 

2/ the kernel logs contain a bunch of these

[   11.925160] ath10k_pci 0000:02:00.0: Direct firmware load for ath10k/fwcfg-pci-0000:02:00.0.txt failed with error -2
[   11.934369] ath10k_pci 0000:02:00.0: Falling back to user helper
[   12.240730] firmware ath10k!fwcfg-pci-0000:02:00.0.txt: firmware_loading_store: map pages failed
[   12.248717] ath10k_pci 0000:02:00.0: Direct firmware load for ath10k/pre-cal-pci-0000:02:00.0.bin failed with error -2
[   12.258861] ath10k_pci 0000:02:00.0: Falling back to user helper
[   12.648875] firmware ath10k!pre-cal-pci-0000:02:00.0.bin: firmware_loading_store: map pages failed
[   12.658402] ath10k_pci 0000:02:00.0: Direct firmware load for ath10k/QCA988X/hw2.0/ct-firmware-5.bin failed with error -2
[   12.668011] ath10k_pci 0000:02:00.0: Falling back to user helper

I assume it's hunting for a valid wireless driver... it seems to fail about 6 times before succeeding?

Any advice appreciated,
br,
btsimonh

a note, I've updated to 21.02.0-rc1, and have uptime > 26 hours.