Bosch SMS6092 w Aqua-Stop programmes stop intermittently

Dishwasher Bosch SMS6092/14, FD-number 7406 035785 (and 0730 101 757).
Purchased new in Belgium in 1995 (22+ years ago) and includes the original Aqua-Stop.
It has been running in the same installation in Skipton for 20 years, on very soft water (8mg/l calcium) – so no salt or rinse aid has been needed or used throughout that time.
Water pressure seems to be adequate / normal (the kitchen tap, fully opened, sprays water out of the sink).
Since around 5 or 10 years ago(!), filling makes a loud hissing sound (that it didn’t before), and takes significantly longer than before.
Cycles of all programmes always take much longer than advised in the manual; for example, the 55degC Economy wash (that we nearly always use) takes about 2h50m, whereas the manual advises about 60m, give or take first filling.
We are careful to scrape plates and keep the filters clean.
A few months ago, the programme stopped mid-cycle, just after draining and before filling (as I recall). Opening and vigorously closing the door was enough to resume the cycle (and often still is). Since then, the mid-cycle stopping has continued intermittently, at different stages in the cycle, and in different programmes. Sometimes opening and closing the door has not triggered resumption, and nor has powering off and on.
Applying very slight clockwise torque to the timer dial sometimes triggers resumption, even before the next click, but I suspect this can disrupt the cycle, perhaps skipping a stage.
As for today, on the 55degC Quick wash, the cycle stopped before the first fill, and would only resume when I slightly advanced the timer dial. However, it skipped the fill, and began the washing stage (opening the dispenser). So I aborted the cycle and tried again. Thereafter, it stopped several more times, never filling. Each time, it would only resume if I advanced the dial. Apart from being useless in terms of dishwashing, I now suspect this was risking the machine’s health. I then tries a Pre-rinse, with the same problems.
I spent quite a few hours researching the matter on UK Whitegoods before trying another Quick wash, which went straight through without a hitch!
As the issue will surely recur, and the machine ought to last at least another quarter century, please kindly advise.
Yours, Paul