strange behaviour on mounting filesystems on boot

Once in a while (3 boots in 7) not all mount points are mounted on boot.
Code:kimera:/home/miguel # mount | grep btrfs
/dev/sda4 on / type btrfs (rw,relatime,ssd,space_cache,subvolid=267,subvol=/@/.snapshots/1/snapshot)
/dev/sda4 on /.snapshots type btrfs (rw,relatime,ssd,space_cache,subvolid=266,subvol=/@/.snapshots)
/dev/sda4 on /boot/grub2/x86_64-efi type btrfs (rw,relatime,ssd,space_cache,subvolid=264,subvol=/@/boot/grub2/x86_64-efi)
/dev/sda4 on /boot/grub2/i386-pc type btrfs (rw,relatime,ssd,space_cache,subvolid=265,subvol=/@/boot/grub2/i386-pc)
/dev/sda4 on /home type btrfs (rw,relatime,ssd,space_cache,subvolid=263,subvol=/@/home)
/dev/sda4 on /opt type btrfs (rw,relatime,ssd,space_cache,subvolid=262,subvol=/@/opt)
/dev/sda4 on /root type btrfs (rw,relatime,ssd,space_cache,subvolid=261,subvol=/@/root)
/dev/sda4 on /srv type btrfs (rw,relatime,ssd,space_cache,subvolid=260,subvol=/@/srv)
/dev/sda4 on /usr/local type btrfs (rw,relatime,ssd,space_cache,subvolid=258,subvol=/@/usr/local)
/dev/sda4 on /var type btrfs (rw,relatime,ssd,space_cache,subvolid=257,subvol=/@/var)
/dev/sda4 on /tmp type btrfs (rw,relatime,ssd,space_cache,subvolid=259,subvol=/@/tmp)
kimera:/home/miguel # mount -a
mount: /home/miguel/Downloads: /dev/sdc2 already mounted or mount point busy.
kimera:/home/miguel # mount | grep btrfs
/dev/sda4 on / type btrfs (rw,relatime,ssd,space_cache,subvolid=267,subvol=/@/.snapshots/1/snapshot)
/dev/sda4 on /.snapshots type btrfs (rw,relatime,ssd,space_cache,subvolid=266,subvol=/@/.snapshots)
/dev/sda4 on /boot/grub2/x86_64-efi type btrfs (rw,relatime,ssd,space_cache,subvolid=264,subvol=/@/boot/grub2/x86_64-efi)
/dev/sda4 on /boot/grub2/i386-pc type btrfs (rw,relatime,ssd,space_cache,subvolid=265,subvol=/@/boot/grub2/i386-pc)
/dev/sda4 on /home type btrfs (rw,relatime,ssd,space_cache,subvolid=263,subvol=/@/home)
/dev/sda4 on /opt type btrfs (rw,relatime,ssd,space_cache,subvolid=262,subvol=/@/opt)
/dev/sda4 on /root type btrfs (rw,relatime,ssd,space_cache,subvolid=261,subvol=/@/root)
/dev/sda4 on /srv type btrfs (rw,relatime,ssd,space_cache,subvolid=260,subvol=/@/srv)
/dev/sda4 on /usr/local type btrfs (rw,relatime,ssd,space_cache,subvolid=258,subvol=/@/usr/local)
/dev/sda4 on /var type btrfs (rw,relatime,ssd,space_cache,subvolid=257,subvol=/@/var)
/dev/sda4 on /tmp type btrfs (rw,relatime,ssd,space_cache,subvolid=259,subvol=/@/tmp)
/dev/sdc2 on /home/miguel/Documents type btrfs (rw,relatime,space_cache,subvolid=266,subvol=/miguel/Documentos)
/dev/sdc2 on /home/miguel/Downloads type btrfs (rw,relatime,space_cache,subvolid=267,subvol=/miguel/Downloads)
/dev/sdc2 on /home/miguel/Pictures type btrfs (rw,relatime,space_cache,subvolid=275,subvol=/miguel/Imagens)
/dev/sdc2 on /home/miguel/Misc type btrfs (rw,relatime,space_cache,subvolid=269,subvol=/miguel/Misc)
/dev/sdc2 on /home/miguel/Music type btrfs (rw,relatime,space_cache,subvolid=270,subvol=/miguel/Musica)
/dev/sdc2 on /home/miguel/ProgramasRFB type btrfs (rw,relatime,space_cache,subvolid=271,subvol=/miguel/ProgramasRFB)
/dev/sdc2 on /home/miguel/tmp type btrfs (rw,relatime,space_cache,subvolid=272,subvol=/miguel/tmp)
/dev/sdc2 on /home/miguel/Videos type btrfs (rw,relatime,space_cache,subvolid=273,subvol=/miguel/Videos)
/dev/sdc2 on /home/miguel/src/UPSData type btrfs (rw,relatime,space_cache,subvolid=595,subvol=/miguel/src/UPSData)
/dev/sdc2 on /var/lib/transmission type btrfs (rw,relatime,space_cache,subvolid=858,subvol=/transmission)
kimera:/home/miguel #As you can see, Code:mount -a mounts the remaining FS.
There is that message about Downloads is busy but I can't figure out why.
I've tried Code:fuser /home/miguel/Downloads before the mount command, but it showed nothing.
I already tried to comment that Downloads line in fstab and the problem persist, except there is no more messages when Code:mount -a.

Any ideas ? As I said, it not happens all the time. Even more strange, when it happens, a simple reboot command cause the next boot to mount all FS, as expected;

Running openSUSE tumbleweed, currently with kernel 5,7 but that already happened on previous kernels.