It could be that NPS is not responding which is the same net effect as a denial. There are also other NPS logs that may not be enabled for whatever reason which may help.
https://learn.microsoft.com/en-us/troubleshoot/windows-server/networking/troubleshoot-network-policy...
You can do a packet capture on the NPS server to make sure you are getting the radius traffic and if you are what responses are (or aren't) being sent. If the requests are getting to NPS and NPS isn't responding or is sending back denials you at least know you have a Microsoft side issue. If the packets are occasionally not getting to the server at all, may need to check along the traffic path to see where they may be dropped.
If you found this post helpful, please give it Kudos. If my answer solves your problem please click Accept as Solution so others can benefit from it.