If your network printer is printing gibberish and random characters that is a common driver-related issue.
I had this problem on Ubuntu and Linux Mint with my Samsung M2070 printer connected over Wi-Fi network.
When I tried to print some single-page document, the printer went crazy and printed out a series of strange random symbols on multiple sheets.
Network Printer Prints Gibberish
My issue with the network printer printing random characters like below has been fixed by manually re-adding it with the “LPD network printer via DNS-SD” protocol:
Start the “Printers” from an application menu or from the terminal:
Click on “Add”, go to “Network Printer” -> “Find Network Printer”, wait for a couple seconds until your printer is found, click on it, select the “LPD network printer via DNS-SD” connection type and click on “Forward”.
On the next windows, select the printer’s vendor, model, give it a name and click on “Apply”.
Print a test page to see if it worked.