raino:
Sounds like you are confusing 2 different concepts - this is very common BTW because of the way things are named.
First there is no such thing as Linear Mode, however there is a Linear Timebase (and a Musical Timebase).
Musical Mode only applies to audio files and it is either on or not. If it is off the length of any Audio Event based on that file will not change as the Tempo changes (you’d want this for a gunshot cue for video). If Musical Mode is on then the Audio Event will expand and contract with the Tempo (you’d want this for a vocal part).
Musical/Linear Timebase only applies to Tracks- both MIDI & Audio. This controls which timeline (Minutes/Seconds or Bars/Beats) the Events & Parts on the Track are anchored to. Say at tempo X bar 8 is at 5:00 seconds. If you opened 2 Rulers, one Bars the other Seconds, and put a Part on a Track at bar 8 then you can see how these work. When you change the Tempo you’ll notice the relationship between the Rulers also changes. If the Track is in Musical Timebase the part will always stay on bar 8 although where it is in mm:ss will change. But if the Track is in Linear Timbase then the Part will always be at 5s but its location in Bars/Beats will change.
Several things can mess up how Musical Mode works. Cubase fairly often doesn’t get the tempo of the Audio File correct (even though you just recorded it at 110bpm in Cubase ). Make sure to verify and set the tempo to the correct value before turning on Musical Mode for the file. If you have something like a comped vocal where you’ve used clips from different takes those can cause issues especially if the same audio is used in multiple sections, like a repeated chorus. That can cause Cubase to try and stretch the same bits of audio differently. The solution, as you found, is to render and work on a clean audio file.
There are several threads here that cover the nuances of this in detail. Worthwhile to search them out.
…and this is a really good explanation as to how it works (and how to understand it better).
To the OP, seriously read through this and carry out raino’s suggestions until the concepts (which aren’t obvious until you understand them) click into place.