I have both an iPhone XR and a Samsung Galaxy S9 (both on latest OS & Spotify Versions).
This seems to be a recent problem, but my password contained an 'x' in between 2 numbers (e.g. 3x5) and it looks like your password field is automatically converting that to a different character (UTF multiplication sign?) - therefore I couldn't log in on either Android or iPhone - had to reset my password to something else. Tried putting in other characters/spaces and deleting them but the field is doing the conversion automatically.
It seems that the conversion (3 x 5 --> 3x5) is occuring in this text box too. Might want to disable that for passwords.