Samsung CLP-500 cutting off print

Re Replace toner message.

Do an information print (MENU, ENTER, ENTER)
This will tell you the pagecount of the various units of the printer

Imaging Unit (Drum)
Transfer Belt (ITB)
Transfer roller
Fuser
Toner Cartridges

etc

The counter for the Cyan toner will simlpy indicate that this is near, at, or over the 'capacity' for this cartridge.

There are
1.5k colour and 2k black 'starter' cartridges
2k colour and 3k black 'standard' cartridges
and
5k colour and 7k black 'high capacity' cartridges.

NOTE even if you only have a single dot of (say) cyan on a page, the counter for that colour will be increased by 1 when that page is printed. 'Empty' cartridges are often far from empty in reality, ans there is no toner sensor, just the counter, which is reset when you install a new cartridge.

The missing print on one side of the reverse side of duplex printed pages is quie a puzzle, as the duplexer simply turns the paper over and presents it to the transferbelt and transfer roller for the second side.

Check the transfer roller is in place properly (open the duplex door - black foam roller A4 width with purple plastic tab on one end black on the other).

Is the duplex door fitted correctly, does it close correctly ?

The duplexer is bad or needs to be realigned, shake up the cyn color. it mostly likely low.