Analogue systems

Hi, I'm new to the list.

I have some AS modules in a Doepfer portable suitcase
(alongside with Doepfers and Cwejmans).
I use my system live as bass synth.

Some weeks ago my AS Oscillator RS95E did that strange thing:
Suddenly the tuning fell down a fifth!
During the soundcheck it was OK, like for months, and after some gigs,
but before we started the show, it was tuned a fifth below
(exactly a perfect tuned fifth below).
It has stayed that way since then.

Isn't it strange? Or it isn't?

Some has had similar behaviour?

Have I to fear that happening again?

Maybe some component is ill?

Thanks for your help in advance

Genís
Austrohungaro
Barcelona, Spain