MAAS regiond allocates an increasing amount of memory

We discovered this when we stop with restart of MAAS regiond services every night for backup of DB.
I can see this behaviour both in 2.7 and after the upgrade to 2.9.1, upgraded 2021-02-01.
And after that we stoped restart of MAAS region services every night.

And it is only one of the regiond processes that use a increasing amount of memory.