PBR rules going away

[Res Cogitans]

I'm having a recurring problem with policy-based routing rules disappearing. My rules are set up by a simple openvpn client route-up script:

admin@RT-AC68U:/jffs/scripts# cat route-up.sh

#!/bin/sh

ip route add default via $route_vpn_gateway dev $dev table 42
ip rule add from 10.10.10.11 lookup 42

This works fine. The problem is that after a while, usually overnight, the ip rule just goes away:

admin@RT-AC68U:/jffs/scripts# ip rule
0:      from all lookup local
32765:  from 10.10.10.11 lookup 42
32766:  from all lookup main
32767:  from all lookup default
# --- overnight time gap here
admin@RT-AC68U:/jffs/scripts# ip rule
0:      from all lookup local
32766:  from all lookup main
32767:  from all lookup default

The VPN connection stays up the whole time. Any ideas what might be going on?

3.0.0.4.376.48_1 on a RT-AC68U.

Thanks.