How are high voltage reed relays supposed to degrade? The contacts are hermetically sealed, the coil is potted, outside of failure modes it never switches current.
The list of possible failures is very very long.
It is a really big mistake to take relays as a simple coil'n'switch.
Relay reliability and switching dynamics are a really very complex topic, also depending a lot on the environment, especially the source and load transient response and impedances.
Even high end sealed HV relays fail, an example :
https://www.spcd.space/proceedings/2018/1st%20Day/Lessons%20Learned%20and%20In-flight%20Experiences/Presentation/05.%20Relays%20Failures.pdfWhat is crazy is that even ESA could identify a root cause only for half of the observed relay failures
And they put in real means to try to get to the bottom of the rabbit hole.
outside of failure modes it never switches current.
Wrong. An AC disconnect relay switches current on every cycle (1-5 per day in a solar inverter)
The X and Y-capacitors will be charged by a high inrush current on every switch closing, typically a microsecond scale spike of 300A if the switch closes on the max AC peak.
That erodes contacts, especially fine contacts that would not be engineered for high currents.
If a DC-link cap is also charged at that moment, it becomes approx 100x worse.
The effects, lifetime, and failures can never be fully validated and guaranteed, because of the random variation in cable length and inductance on the AC network, among others like mounting angle affecting spark rising......