local openntpd-servers fail to sync for DAYS - help

[DawgG]

i'm running to local openntpd-servers so local clients can sync their clocks with them but recently they drop out of sync FOR DAYS so the clients are not allowed to sync and a lot of them show the wrong time (which must not happen). first i suspected it is the clients' fault https://forums.gentoo.org/viewtopic-t-711905-highlight-openntpd.html, but obviously, it istn't.

the two local servers are connected to the net via a nat-firewall and a 2mbit line. they've been working fine for at least two years now. today, they've been out of sync since last friday and i have found no way to force them to sync (different servers etc.) i just never get the message "clock is in sync now."

what is wrong here? is openntpd TOO simple and lightweight after all?
or are there too many servers in the configs? just using "europe.pool.ntp.org" results in "no reply received in time" even though it's reacheable w/out problems.

ntpd.conf server 1:

[VinzC]

I've also tried openntpd a while ago but I promptly reverted to ntpd, much more stable and reliable. There are a couple of articles that put the doubt over openntpd.
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