aaahhhh - yes

I found the Problem: It seems there was a loop! Some of my parents did have their own childs/variants as related products (I found it nice to see all the child products under product-details and it worked in 2.0.14)!
Solution: I deleted all entrys in table virtuemart_customfields relating to the id from virtuemart_customs (RELATED_PRODUCTS) and see:
everything works fine now. I can edit every other product as a related product, but no product own childs/variants, then fatal appears again.
Now it´s clear for me that this config does an loop because childs refer to the related products from their parents if you doesn´t check override parents-customs, so it´s an neverending loop and only limited to php_memory_limit ...
I am so glad, I thought I have to start from begin ...
What I else noticed is the max improved performance from 2.0.14 to 2.0.22 and a decrease of SQL-queries in FE! Glad to see all the new functions! Great, great great!
Thanks to all vm-buddies who helped out in this threat
best regards
jens