I have a similar problem.
I'm losing pressure somewhere towards the head/cap. I've tried the cap adjustment as listed above.
When the machine (JV400LX) starts in the morning it thinks it has run out of ink and displays all red lights on the cartridges.
I usually have to do a few cleans or a damper fill up to clear this - with the associated machine restarts.
Mimaki techs just up the cleaning interval (to every 15mins) and upped the level to reduce the nozzle dropouts during print.
I have replaced both capping stations but no change has been noticed.
The machine used to do this there was a build-up of dried ink around the heads (preventing a good seal at the cap i assume), but this is not the current issue.
I have also put the machine up on form ply to level the floor which helped for a while.
The printers have always been kept in an airconditioned insulated room. The aircon runs at 21 degrees.
Every time the printer was serviced by Mimaki tech's they made this problem worse. Usually, after a scheduled visit the techs would have to return 2 or 3 times to get everything to reseal especially when changing dampers.
The printer doesn't get used excessively but does get used regularly.