Gathering some problems / errors of the status quo in this issue:
1) Loadwallet error
Creating a wallet while using Spectrum generates a JSON file but doesn't save the wallet file on the Core node (obviously) since it uses the database to store the wallet data.
Therefore, when you switch back to using the Core node you get this error:
Gathering some problems / errors of the status quo in this issue:
1) Loadwallet error