L2TP unstable on Dual WAN load-balancing configuration

Hi there,
I use the last 378.55 firmware by Merlin on Asus RT-AC66U.
In the case I setup a load-balancing config for 2 ISP:
- ISP1 - Automatic IP
- ISP2 - L2TP
The config works well by time to time router losts L2TP connections and cant get BRAS.. On the log it looks like
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Sep 25 10:24:15 /usr/sbin/l2tpd[1095]: tunnel_establish: gethostbyname failed for 'tp.internet.beeline.ru'
Sep 25 10:24:25 /usr/sbin/l2tpd[1095]: tunnel_establish: gethostbyname failed for 'tp.internet.beeline.ru'...

L2TP unstable on Dual WAN load-balancing configuration