There is a serious problem with the core daemon, that should be attent to.

When you use z_exportwallet to export the wallet and import it on another device. Shielded transactions cannot be unshielded anymore! You will get the error Witness for note commitment is null.

This problem also seem to exist in the ZCash core, and it's still an open issue! See: https://github.com/zcash/zcash/issues/2524

The issue causes homepool currently not to be able to pay miners as shielded funds are locked into shielded addresses! Please attent to this serious issue!