[Bug]: ${fs_*} variables don't work with mergerfs (fuse)

[hujuice]

What happened?

I'm using mergerfs (https://github.com/trapexit/mergerfs) to combine two large storage disks. It works smoothly for me, including the df output.

/dev/sdb1                                                  3.6T  3.2T  260G  93% /storage/TOSHIBA-DT02ABA400
/dev/sda1                                                  3.6T   36K  3.4T   1% /storage/WDC-WD40PURZ-85AKKY0
WDC-WD40PURZ-85AKKY0/Foto/raw:TOSHIBA-DT02ABA400/Foto/raw  7.2T  3.2T  3.7T  47% /foto/raw/archive

At least ${fs_bar} and ${fs_used_perc} don't work for me. They show 0.

Mergerfs is a unionfs based on FUSE.

Note
The "device" name in fstab is quite long (in my case, /storage/WDC-WD40PURZ-85AKKY0/Foto/raw:/storage/TOSHIBA-DT02ABA400/Foto/raw). mount and df shorten it removing the first, common part.
In conky I tried both ways.

Version

1.19.6

Which OS/distro are you seeing the problem on?

Gentoo

Conky config

${fs_bar 4,60 WDC-WD40PURZ-85AKKY0/Foto/raw:TOSHIBA-DT02ABA400/Foto/raw} ${fs_used_perc WDC-WD40PURZ-85AKKY0/Foto/raw:TOSHIBA-DT02ABA400/Foto/raw}%

Stack trace

No response

Relevant log output

No response