implicitclass returned status 4/7

Describe the bug
I have used the driverless for a while. And the driverless is added manually by the command
lpadmin -p <foo> -v <ipp-address> -E -m driverless:<ipp-address>.

However, I have never been able to successfully print out the driverless added by the cups-browsed.
Today I upgraded to Ubuntu 25.04，the issue still exists. Of course the problem also exists on my other Linux distros.

I'm quite busy recently and don't have enough time to do a deeper investigation, so only create the issue first.

System Information:

• OS: [Ubuntu25.04]
• cups-browsed [2.1.1]

Additional context
Error log:

W [18/Apr/2025:16:25:47 +0900] [Job 233] Backend implicitclass returned status 7 (retry job immediately)
D [18/Apr/2025:16:25:47 +0900] [Job 233] No free destination host found by cups-browsed, retrying in 5 sec.
W [18/Apr/2025:16:25:52 +0900] [Job 233] Backend implicitclass returned status 7 (retry job immediately)
D [18/Apr/2025:16:25:52 +0900] [Job 233] No free destination host found by cups-browsed, retrying in 5 sec.
W [18/Apr/2025:16:25:57 +0900] [Job 233] Backend implicitclass returned status 7 (retry job immediately)
D [18/Apr/2025:16:25:57 +0900] [Job 233] No free destination host found by cups-browsed, retrying in 5 sec.
W [18/Apr/2025:16:26:02 +0900] [Job 233] Backend implicitclass returned status 7 (retry job immediately)
D [18/Apr/2025:16:26:02 +0900] [Job 233] No free destination host found by cups-browsed, retrying in 5 sec.
W [18/Apr/2025:16:26:07 +0900] [Job 233] Backend implicitclass returned status 7 (retry job immediately)
D [18/Apr/2025:16:26:07 +0900] [Job 233] No free destination host found by cups-browsed, retrying in 5 sec.
W [18/Apr/2025:16:26:12 +0900] [Job 233] Backend implicitclass returned status 7 (retry job immediately)
D [18/Apr/2025:16:26:12 +0900] [Job 233] No free destination host found by cups-browsed, retrying in 5 sec.
W [18/Apr/2025:16:26:17 +0900] [Job 233] Backend implicitclass returned status 7 (retry job immediately)

Start by reproducing the failure with Ubuntu 25.04 and cups-browsed 2.1.1 using the driverless printer setup in the report. Trace the implicitclass backend and cups-browsed handling of destination hosts when status 7 is returned. Done means identifying why no free destination host is found and adding a regression test for the failing case.