I allowed G’Mic-Qt (3.0.0_pre#211011) to refresh filters from the web, running on Gimp 2.10.28, and then found it promptly removed the Patterns>Stendl filter. I had really rather liked it and been using it for some months on and off. Google Search revealed nothing of the name Stendl. A couple of Reddit users were convinced I had confused it with Stencil…
Hello @Jelf0 ,
To be honest, I’ve never heard of a Stendl filter in G’MIC.
What was this filter doing ?
Filter Patterns / Stencil exists though.
It gave a sort of brain coral look, very slightly reminiscent of Voronoi. I have just under 300 Gimp projects, so it might be rather difficult to find the one I used the filter in, especially since I virtually never use them in isolation. I’m now worrying in case no one, not any one, has ever heard of the Stendl filter! 
Being somewhat OCD, I keep notes on all the filters etc I use; and I made the following notes on that one;
Stendl; (radius 1); rather fascinating ‘brain coral’ effect mapped into image. Doesn’t seem to do well on high luminosity areas. Unfortunately it vanished on updating the G’Mic filters 211123 
Just to plug a possible gap, I never found the Stencil filter of any interest.
Maybe you had added one of the G’MIC filter as a “Faves” and renamed it as “Stendl” ?
I see no other explanations for the moment 
Always possible, I certainly make errors (although I’ve never investigated ‘Faves’ as an option). Thanks for the input.