I don't know if it's ok to change it, but perhaps limiting tmpfs
in /etc/fstab by size= and limiting memlock in /etc/security/limits.conf
has something to do with it and could be changed.
Assumed nobody with the needed knowledge should reply soon, it might be
worth to use "memlock", "ulimit" etc. as search terms for Internet
research.
By default tmpfs takes half of the RAM and a default real-time
limits.conf comes with an unlimited memlock.
Attention, that are just shots in the dark!