Unlikely to be tube(s), as these are practically impossible to damage.
It might be tin whiskers, I’ve seen this once or twice on HV stuff.

Usually if a tube starts to go bad it will oscillate and false count, in
my experience with SBMxx tubes.
A good test is to connect a red LED and 1K resistor in parallel, connected
in series with the tube (on the Hot side!) with wire spirals so as not to
damage the heat sensitive tube interconnect and this will at least visually
show when the tube counts particles.
If the LED is on all the time then the HV might be too high, or other problem.

With alpha tubes such as LND712 if there is a faint red glow inside then the
tube is bad. Intriguingly this does not always apply to all the electrodes
and on multi-electrode tubes ie CBT11A this can be handy to know.