Topping up gas once every 2 years is still acceptable.
I think you can ignore it and just top up.
If it happens < 6 months once, then maybe you can consider to do some repair works to it.
Sigh, previous gas top-up last < 1mth, left 4 bar.
Considering leak-test to determine if leak is due to
- equipment (4yr old Mitsu sys4)
- piping (95% new R410a piping, <10% reuse R22 piping).
Is it usual for piping leak to develop so quickly/suddenly over 2 months?