I always do manual persistent mapping of all my serial USB ports, I find that this ensure that I do not get USB issues. I am running Stellarmate on a RPi4 setup as a dev machine (all the dev libraries are loaded).
These are my rules:
SUBSYSTEM=="tty", ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6015", ATTRS{serial}=="DN03TK6K", MODE="0666", SYMLINK+="sestosenso"
SUBSYSTEM=="tty", ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6001", MODE="0666", SYMLINK+="eqmodmount"
SUBSYSTEM=="tty", ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6015", ATTRS{serial}=="PA3FGTR8", MODE="0666", SYMLINK+="pegasusdmf"
SUBSYSTEM=="tty", ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6015", ATTRS{serial}=="PPB3C185E", MODE="0666", SYMLINK+="pegasusppb"
SUBSYSTEM=="tty", ATTRS{idVendir}=="0403", ATTRS{idProduct}=="6015", ATTRS{serial}=="UPB25H0XWD", MODE="0666", SYMLINK+="pegasusupb"
SUBSYSTEM=="tty", ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6015", ATTRS{serial}=="D3090FN1", MODE="0666", SYMLINK+="ioptrongem45"

Everything works fine except the "pegasusupb" link. I can access it fine on ttyUSB1 but I would really like to use the link name just to ensure I don't run into problems.
I got the serial ID from udevadm as usual.
I have a suspicion that it stopped working after I loaded the libraries I need to setup the dev environment.
The only difference with the UPB is that it is the only device plugged into a RPi4 USB port. All the other devices are connected to the UPB.

After I restart with these rules I do not see the pegasusupb in /dev

Any suggestions?

Ignore. It was a typo. In my file I have "idVendir" and not "idVendor".
Sometimes just posting solves the problem. I must use a larger font size!