update: last couple of days it seems to be going ok.
Did not update yet to 2.0.3 prerelease, also reverted back from all previous modifications.
What seems to be working: in "System\Routing\GW_WAN" under 'Advanced' I increased the value 'Down' to 60 (default was 10). This action seem to have helped for the dyndns update, I haven't had the nasty 'curl' error anymore since modification. So either it actually helped, OR I have been lucky until' now. I still sometimes see the GW as Offline, so maybe I should double it. (maybe I need some better understanding of the apinger mechanism :-[ )
As 2nd backup mod, I installed the cron package & modified the nightly scheduled DynDns check to run every 30 minutes. It does pollute the system log a bit, but good side effect is I can check how it is working, and so far it seems I haven't needed the cron mod yet.
before I forget: Tnx Tim & Phil for the given suggestions! Really appreciated…