Inconsistent Router Advertisements - sometimes only contain the prefixes and no other options

I noticed odd behavior of some systems not immediately obtaining DNS servers after reboot/wakeup from sleep. After looking at what RAs are actually being sent I noticed that VyOS is sending RAs that only contain the prefixes every 10 seconds, even though my config does not contain any custom interval and the default is 0.33*600 - 600 according to the radvd docs. (And also according to the actual written /run/radvd/radvd.conf)

# show service router-advert | strip-private
 interface bond0.100 {
     dnssl xxx.xxx
     link-mtu 1492
     name-server xxxx:xxxx:xxxx::53:1
     name-server xxxx:xxxx:xxxx::53:2
     prefix ::/64 {
         preferred-lifetime 7200
         valid-lifetime 86400
     }
 }
[...]

Matching the actual interval of radvd (every ~250-500s), I get RAs that contain not only the prefix but also the DNSSL, MTU and RDNSS. I also noticed that Router Solicitations are also answered with short RAs, lacking all options except the prefixes.

Any clue where the RAs every 10s come from and why Solicitation also get short answers?

VyOS Version: 1.4-rolling-202205200217