Webhooks that come from analysis are sent by the Compute Engine – turning up sonar.log.level.ce should let you see if anything is going wrong in the CE (ce.log). It will at least help in starting to troubleshoot.
2022.05.23 10:58:34 DEBUG ce[AYDwI6eyV6zp2JrtPane][o.s.s.w.WebHooksImpl] Sent webhook 'test' | url=https://webhook.site/e50fe798-dab5-4fc8-ba59-5f16de8195ae | time=380ms | status=200
2022.05.23 10:58:34 DEBUG ce[][o.i.c.TaskRunner] Q10000 starting : OkHttp ConnectionPool
2022.05.23 10:58:34 DEBUG ce[][o.i.c.TaskRunner] Q10000 run again after 300 s : OkHttp ConnectionPool
2022.05.23 10:58:34 DEBUG ce[][o.i.c.TaskRunner] Q10000 finished run in 285 µs: OkHttp ConnectionPool
2022.05.23 10:58:34 INFO ce[AYDwI6eyV6zp2JrtPane][o.s.c.t.p.a.p.PostProjectAnalysisTasksExecutor] Webhooks | globalWebhooks=1 | projectWebhooks=0 | status=SUCCESS | time=413ms