High memory usage on GT-AX6000 - how to diagnose ?

[SR-G]

In the meanwhile :
- i rebooted my router
- i shutdown the recommended service
- i activated the diversion cache drop once a week
and my memory usage was still slowing increasing from ~55% (after reboot) to ~81% (today).

So i tried the purge command above, and indeed, it definitely recovers some memory :

free && sync && echo 3 > /proc/sys/vm/drop_caches && free


             total       used       free     shared    buffers     cached
Mem:       1018848     808408     210440      34804      75796     197504
-/+ buffers/cache:     535108     483740
Swap:            0          0          0

             total       used       free     shared    buffers     cached
Mem:       1018848     591832     427016      34804        412      64056
-/+ buffers/cache:     527364     491484
Swap:            0          0          0

Note :
- i do have a 32GB USB disk plugged in with SMB activated (but it does not explain the slow increase over time).
- AIProtection is and has always been disabled