Maybe even a bug in the switch/nic driver...
no, everything seemed to work ... as said on v21 this is not happening. so, i believe it is a bug somewhere 
Some tests that, assuming are possible, could help but will require manually compiling.
- Compile and test pppd version from Openwrt 21.02 (2.4.8) on 22.03
- Compile and test pppd version from Openwrt 22.03 (2.4.9) on 21.02
That would confirm or discard the pppd part.
From what I can see, there is only 1 commit updating the ppp version between the branches.
what about force install pppd.ipk? or due to kernel version binding it would not work anyhow?
I'm not sure that would work, that's why I mentioned recompiling.
am struggling with compiling pppd version other than its owrt official bundled version.
"only 1 commit" looks not that simple (to me) as git checkout tag/Y; git checkout tag/X -- package/network/services/ppp breaks compilation as pppd patches do not apply. I'd need the time to re-align patch codes which i do not have so will stick to v21 as v22 gives no benefit - to me - i think.
thanks everyone for the ideas.