Mamiya 645 Pro TL metering is off

Just purchased a Mamiya 645 Pro TL, with the 80mm f/1.9 lens, a motor grip and FE401 prism finder.
Last week, the metering seemed to work properly.

This afternoon, the metering suddenly didn't work. Each time I half-pressed the shutter, no red indicator shown in the prism finder. When shooting in A/AEL mode, the shutter won't fire. No problem so far when shooting manually, though.

Already did the battery check. The red indicator above the "PRO TL" lit, which means the battery is still OK.

Anyone ever experienced this?

Check and clean the contacts for the battery, the finder and the back.

I did that. I cleaned all of those yellow connectors with clean tissues.
As far as I can tell, those connectors look normal.

But the metering is still off. Well, guess I have to use a handheld lightmeter then...