Thoaght I already did…twice.
In the enroute phase you can file a flight plan that while keeping you clear of cumulus granite may be too low for a IFR route segment that it follows, too low for a sector altitude or too low for a MCA that the built in sim uses to calculate how high to keep you.
ATC will then send you higher to some “calculated altitude” for a few miles…as terrain or what ever limiting factor below you drops away it may then clear you again for a lower altitude or the one you filed.
A few minutes later the next rising terrain etc will have you send back up again.
You can avoid most of this by actually planning a route using proper IFR planning charts etc OR you can try to simply use the method I suggested. Ask for an increase to your filed altitude close to what ATC gave you and hope for the best.