Master fader: right channel not indicated (-inf)

[Bombs'n'Away]

I've been working on a project for some hours when all of a sudden I realized that my right speaker channel's peak is not being indicated anymore by the master bus. The peak meter says "-inf" for the right side during all of the project.
Sound is coming out of the speaker correctly. I did not change the master send/main hardware output, I checked all plugins and I closed and restarted Reaper - nothing helped so far. I have been using the Default_5.0_AGYR theme without problems for weeks and have not changed that recently.

Edit: Can be closed. Right click the master bus in the meters section, untick "multichannel peak metering" and both channels' peaks appear as usual. I do not know why this was active all of a sudden.