EUREKA! I found the solution to the problem of my computer not seeing the printer even though they were connected to the same network.
Some system update must have changed the File and Printer Sharing setting. I did not initially think to check this, as I certainly did not change it myself. However, I found that it had been turned off, so I turned it back on and was able to reinstall the printer.
BUT (there's always a 'but'), I do not know if my first problem, the intermittent loss of connection to the printer, will continue to occur. It will take time to determine that.