Printer redirection not working

We’ve been using the NET USE command to setup remote printers to redirect printing to LPT ports. It’s been working for years except for occasional instances when the NET USE connection would DISCONNECT. I now have a couple of these same users print to their long standing printers, it goes through the motions of printing (hits the print queue then disappears) but no reports. They can print to the printers locally, using a separate printer definition (using IP address instead of LPTn). What could be the issue?