This is why we have fstab - we define exactly where the drive mounts every time, also whether it mounts at boot or only when selected.
When I mount my WD disk, it always appears as /run/media/user/W2 and never /run/media/user/W21. I cannot imagine why it would…
Now there’s another option, rather than using fstab.
To get a feeling/idea for this, you can look in /run/systemd/generator for a mounted disk. You’ll see an entry (usually created from fstab) in the form of a file.
For example, my disk /dev/sdb1 is mounted at /mnt/T3.
There is a file created called ‘mnt-T3.mount’ the name replacing the slash with a hyphen for the name and location you want, be it /mnt/T3 or /data/T3 or whatever you like.
cat that file and I find this information:
Automatically generated by systemd-fstab-generator
So you can use systemd to mount your disk as you require by creating a file (using by-label or by-UUID as you please) in the location /etc/systemd/system/mnt-T3.mount (the name of the file following the rule for converting the mount location).
Basically, /run is a volatile structure created at boot, and apparently /mnt is also primarily intended as a temporary mount but I never bothered to change it. I’ll look into that when my faulty SSD is replaced and I have an excuse to mess about.
I see no logic in saying you don’t want to change the mount point of your second drive, when you clearly have issues requiring a fixed and reliable mount point.
I see an extra benefit, once sorting out the mount point using something like ‘gnome-disks’ and ‘fstab’ to actually create these systemd mount points yourself.