Cloud armor request.path.startswith lets traffic bypass random

Question

In Google Cloud Armor I have multiple rules (+50). Below is the one with lowest priority number. It is based on bad_path URI example in Cloud Armor documentation

request.path.startsWith('/api/foo')
Deny 403
Priority: 1
Activated 1st November

In Google cloud logging, I believe the rule can be bypassed:

resource.type:(http_load_balancer) AND
jsonPayload.enforcedSecurityPolicy.name:(rules) AND
log_name="projects/foo_bar/logs/requests" AND
httpRequest.requestUrl="https://foo.example.io/api/foo" AND

The request pattern is:

https://foo.example.io/api/foo

The data below are sampled from 2 minutes:

Outcome	statusDetails	http status	Priority	requestMethod	RequestSize	timestamp	receiveTimestamp
Deny	denied_by_security_policy	403	1	POST	1188	12:49:48.746858Z	12:50:24
Deny	denied_by_security_policy	403	1	POST	1191	12:49:48.297242Z	12:50:02
Allow	response_sent_by_backend	200	60000	POST	1189	12:49:48.924442Z	12:50:36
Deny	denied_by_security_policy	403	1	POST	1189	12:49:48.924468Z	12:50:29
Deny	denied_by_security_policy	403	1	POST	1184	12:49:48.990177Z	12:49:50

The below fields are same for all requests:

backend_service_name: Same for all above
forwarding_rule_name: Sane for all above
url_map_name: Same for all above

Example of 403 httpRequest

httpRequest: {
 latency: "0.1"
 remoteIp: "x.x.x.x"
 requestMethod: "POST"
 Requestsize: "1200"
 requestUrl: https://foo.example.io/api/foo
 responsesize: "315"
 status: 403
 userAgent: "XYZ"
}

Example of 200 httpRequest

httpRequest: {
 latency: "0.5"
 remoteIp: "x.x.x.x"
 requestMethod: "POST"
 Requestsize: "1202"
 requestUrl: https://foo.example.io/api/foo
 responsesize: "3150"
 serverIp: "x.x.x"
 status: 200
 userAgent: "XYZ"
}

In Google cloud logging (audit logs)

cloudaudit.googleapis.com%2Factivity
resource.type="network_security_policy"

There are 3 cloud armor updates, but they are all a few hours after the timestamp above.

Rule	ValidateOnly	Resource	timestamp	receiveTimestamp
2500	true	network_security_policy	14:02:03	14:02:04
2500	N_A	network_security_policy	14:02:05	14:02:06
N_A	N_A	network_security_policy	14:02:11	14:02:12

What more steps can I take to understand why the rule is bypassed sometimes? The above example is not an isolated incident.

I don't think the "Cloud Armor POST body inspection limitation" is relevant here.