I have investigated the problem further and the problem is caused by
"driverless" sending get-printer-attributes IPP requests to each printer
it lists, to check the quality of driverless printing support. See
https://github.com/OpenPrinting/cups-filters/pull/235
This makes "driverless" taking too long time, especially if there are
many printers. See the investigations on
https://github.com/OpenPrinting/cups/issues/65
Therefore I have removed the feature again now, on both master and 1.x
branches of cups-filters:
https://github.com/OpenPrinting/cups-filters/commit/3fddcf5
https://github.com/OpenPrinting/cups-filters/commit/aae86d2
Please test, this should solve your problem.
I will release cups-filter 1.28.7 soon, with this change included.
