Azure Application Gateway WAF blocks common ASP.Net Core Requests
OWASP 3.0 works based on the sum of scores which it gets in each rule. A single request will be processed by a set of rules and each rule will add a score to the request and at the end, if the score exceeds a limit, the request is blocked.
In your case, you can read the rule definition here and check what is the score each rule adds to the particular request.
The last rule PCRE limit is the mandatory rule which cannot be disabled was hit because of the score that the request got by other rulesets. So you need to track the other rulesets and disable or create an exclusion to get your site working.