let me try to give some more details
APPI package which is downloaded from the cloud (~3MB) is kept in /fwtmp and may be replaced upon an new APPI update.
The issue was that when the file is being replaced with the new version, in some cases, some processes still kept the original (deleted) file open. This prevented the original file from actually being released, and those ~3MB were still considered as used in the /fwtmp partition.
This decreased the available space in /fwtmp.
this issue require certain scenario to happen, so it's not common, but in any case, issue was fixed on 990173072
990173072 is available in the vSMP for domains that require an upgrade.