(1) Indeed I have seen wording referring to “regulatory changes” that would allow a bank to adjust conditions (or might have been to cancel early on, don’t remember exactly). Bank confirmed in that case that this is in no way related to simple changes of the SNB reference interest rate. Given the political system/landscape in Switzerland, I don’t see this as a risk.
(2) Re-evaluation of your home’s value is absolutely a thing, but that is an entirely different aspect. In today’s market the banks are generally (slightly more) cautious and might set your house’s market value below what you actually pay, i.e. you will have to finance 20% + anything above their internal market value.
(3) “Einzelne Banken formulieren in ihren Verträgen ein Kündigungsrecht für Festhypotheken. Dieses Kündigungsrecht kann die Bank dann anwenden, wenn der Hypothekarnehmer z.B. plötzlich ein schlechteres Einkommen hat.”
Ha, it does exist! Would be interesting to hear which banks try this…
For both 2 and 3, consider reality: As long as you pay your (fixed) interest, the bank has no reason to call a perfectly served mortgage, as they must be aware you might not be able to refinance and they end up with the collateral/house.
The real risk you face is refinancing. You must fulfil then current regulatory requirements, where anything can go wrong, and you might just be out of a job right around that time.
(4) “Am I being paranoid for strongly believing that in the case of a strong increase in interest rates, the bank will try to cancel a low interest mortgage at all costs?”
Yes. Banks of course will have either refinanced your mortgage equally low, or due to lack of refinancing options the will simply not offer you a very long term mortgage. Additionally, you mentioned reputational risks yourself. If you want to be on the safe side, just avoid banks with those extremely unfair examples posted by you (“steht im alleinigen Ermessen der Kreditgeberin”!), and have your main account with another bank (if they are smart enough, suddenly receiving payments from the unemployment agency might trigger questions).
(5) “The Rahmenvertrag can be cancelled anytime. But not the mortgage”: That is standard, and if you would ask about risks of a LIBOR mortgage there would be many more things to consider (esp. as LIBOR will be discontinued, providing an excellent change for the bank to screw you over). For a fixed mortgage, the framework agreement is basically irrelevant.