syz-cluster: mysterious `SYZFATAL: image testing failed w/o kernel bug`

[a-nogikh]

Example: https://ci.syzbot.org/series/b4aa6e49-79ea-440f-b64a-304320faf474

All smoke test output we get is:

timedout after 30m0s ["/syzkaller/bin/syz-manager" "-config" "/tmp/test-workdir/manager.cfg" "-mode=smoke-test" "-vv=2"], exit code -1

2026/04/01 13:56:43 serving rpc on tcp://36207
2026/04/01 13:56:43 pool: booting instance 2
2026/04/01 13:56:43 pool: booting instance 0
2026/04/01 13:56:43 pool: booting instance 1

I wonder if it can be related to #7011