PS4 saves are in a proprietary format. You need (paid, ~$50) or Apollo Save Tool (free, but requires jailbroken PS4). For non-jailbroken PS4:
Some modded gear is "illegal." If the game detects a part combination that literally cannot exist (like an elemental effect on a non-elemental gun), it sometimes wipes it upon loading. Ensure your weapons use valid, albeit rare, part combos.
To transfer saves between the PS4 and your PC.
Go back to Save Wizard . In Advanced Mode, click "Import," select the modified .sav file, then click "Apply." Save Wizard will re-crypt the save with your console's specific keys and re-sign it to your PSN ID.
Yes. The process is the same for the Borderlands: The Handsome Collection version on PS4.
Just remember: With great power comes great responsibility. Don’t crash your friend’s PS4.