For months I haven't been able to login to "My UPS" (which is now the only way to get detailed tracking info). Attempting to login would give me error LASSO_1010. Attempting to reset my password would return an "Application error" and never send a reset email.
The solution (via this Reddit thread) was to install the UPS mobile app, and initiate a password reset from the app. In that case I did receive the reset email, and was able to update my password, and I can now login.