(only) PB Touch HD instable since 2015.11

[hol]

Hello,
I'm new here.
My problem is, that the wonderful program koreader crashes immediately on Touch HD und Touch HD2, but works fine on mostly all other pocketbooks incl. Touch HD 3.
The facts: all versions incl. the 2019.07 works fine on PBs: old lux3, old inkpad 1, touch HD 3, inkpad 3, but not on Touch HD 1 and 2.
On Touch HD 1 (and the very similar Touch HD2) the last version of koreader is 2015-11, which runs perfectly stable.
So I installed & renamed this version as koreader_stable and hopefully try any other version of koreader ... but not successful. The firmware I tried ar the newest, possible the error is firmware-dependent?

My question:
Is it not possible to consider a "general" difference between other Pocketbooks and Touch HD on the one side and koreader 2015.11 and all newer versions?
In crash.log is seen always a segmentation fault, mostly after loading the last plugin wallabag. But no more hints. sometimes I can open a book, but the crash is than shortly after, irreproducible.

Because the hd is a very good reader with all necessary functions, id should be great to find the error and runs a newer koreader ... possible the error is simple, for example a not necessary plugin?
I would help with testing
hol