If the LPR adjustment does not work...
Consider removing the V4 driver and installing the V3 driver.
I have had much better luck with V3 drivers than with the V4 drivers (for many products).
Change driver port to use LPR protocol
1. Using Win10 search feature, type 'printers' into the Search field, and press Enter.
2. Select 'Printers & scanners' from the menu (should be at top, and probably already selected).
3. Find the C400 printer in the list of printers, and left-click it.
4. Choose 'Manage'.
5. On next screen, select 'Printer properties' (left side).
6. Navigate to the 'Ports' tab.
7. The Standard TCP/IP port for this printer should already be selected.
8. Click "Configure Port" button.
9. Setup the port dialog as shown in the pic (the Queue Name setting is lower case LP).
10. Save settings and exit driver dialog.
11. Reboot your computer, then test print when computer is rebooted.
I'll try to post instructions tonight. You have been to that dialog in a previous post on this thread (I think).
It's just a simple matter of changing the setting from RAW to LPR, then using "lp" as the print que, instead of using port 9100 for raw. I think you can alternatively use port 515 instead of using lp, but I'll have to check to refresh my memory.
This step will change the way the the data is sent to the printer which may fix the issue, but will also give further clues as to what is going wrong.
Both of these protocols should be enabled by default at the printer (but im not 100% sure about that on this model).