Key signature added in measure that was previous at start of system does not appear
This is related to this, I think : #279048: Mid score key sig change causes all saves to become unusable, no error message, MS3 hangs. Reference thread: https://musescore.org/en/node/279095
Create a multistave work, add enough notes to create another system. Drop any key change anywhere, and the key sig will be invisible, though accidentals are added to notes. Saving and reloading the score results in odd behavior - it looks like it corrects the score as if the key sig change didn't exist, i.e. adding or removing accidentals attached to individual notes.
The save is attached