I have similar issue but with cli_wallet, it imports 200+ keys from my BTS 0.9.3c key export file. But show no MUSE at all. The same 200+keys allow me to claim my BTS 2.0 stake with BTS 2.0 cli_wallet. This problem exists long time ago since the launch of MUSE blockchain. It seems not solved so far. I wonder if it is because I have too many keys imported at the same time.