Sometimes can't print to B2360dn laser printer

We have a number of Dell B2360dn laser printers.  Two of which are used quite a bit.

Occasionally we can no longer print to one or more of them.  99% of the time it is the two that are used the most.

We are printing using a Redhat Linux system using CUPS.  All the printers are setup on the Linux side to print via socket://{IP}/:9100

When the problem occurs I can no longer connect to the printer using telnet {IP} 9100

I can ping the IP, and telnet to port 80.  I can bring up the WEB interface and reset the printer and then it is fine again until it happens again.

I have seen the problem occur on 4 of the printers.  Currently I have switched one of the busy printers to use the LPD protocol, instead of JetDirect.  It remains to be seen if this solves the problem..

Question:

1) Is there any character or sequence of characters than can be sent to the printer that would cause it to stop accepting connections on port 9100.

2) Is there any kind of out of paper, tray open, or other condition the printer could get into that would stop it accepting connections on port 9100.

3) Anybody else ever seen this issue?

P.S. Also have a coupe Canon printers that are used quite a bit that do not have this problem.

TIA  John