Adding or removing measures when parts are defined doens't work.

Hello,
it is the first time I had extracted parts, so maybe the problem existed before.

FIRST ISSUE: ADDING MEASURES IN A SCORE WITH PARTS CRASHES
How to reproduce.
1. I created a 4-parts score for our choir, with 2 staves (i.e. Soprano-Alto on the treble key, Tenor-Bass on the bass key).
2. I extracted 4 parts so I could export mp3 and midi files for each voice.
3. I noticed that I needed to add a few extra measures.
4. I did ctrl-Insert (to insert a few measures) and added 10 measures.
5. I am able to see the score with the extra measures added for 5 seconds, then Musescore crashes.
It's always reproducible.

Solution :
– Remove the parts.
– Save the score.
– Add the extra measures.

SECOND ISSUE : DELETING MEASURES AFTER THAT IS IMPOSSIBLE
How to reproduce.
I noticed that in the above work where I previously had parts, I had added 2 measures too many
1. Select measures and try to delete them with Ctrl-Delete or the menu
2. Nothing happens.

Solution :
– Save the score and quit Musescore
– Restart Musescore.
– Now it works correctly (i.e. I can add and remove measures without any problems),

SOFTWARE:
OS: Windows 10 (10.0) (French-Canadian), Arch.: x86_64, MuseScore version (64-bit): 3.4.1.9660, revision: 20414b2