Also, I’ve tried everything to reproduce this situation with the wallet, but I can’t replicate it. My spacebar is still malfunctioning, but there’s no way this would have caused a 'none' sighash to be selected.
If not the keyboard or an accidental series of keystrokes.
There's also a possibility that the PSBT is altered/corrupted to prompt the signer wallet to sign with
SIGHASH_NONE type flag before it's signed by Sparrow.
In that case, once the PSBT is loaded to Sparrow, it will automatically select and display
SIGHASH_NONE during the signing process.
However, based from your description of what happened in page2,
post #21 that you've "
sent the transaction directly",
it shouldn't have been an altered PSBT since the transaction creation and signing processes are done in the same machine without the need of transaction export.