Tomcat's Catalina utility threads are periodically using high CPU and memory

We have a webapp that uses on average 20% CPU when idle, with no network traffic or any kind of requests. It is running on Java 11, Tomcat 9, Spring Framework 5.3, Hibernate 5.4. However the issues I will describe below were true on Java 8, Tomcat 8.5, Spring 4.3 and Hibernate 4. as well. I tried to profile the application using JFR and JMC, and I experimented with a lot of configurations. In the image above it looks like catalina-utility-1 and catalina-utility-2 threads wake up periodically and for a few seconds use a lot of CPU. Also there seems to be a huge amount of memory allocations done by these threads, 30+ GB in total in the sampled 5 minutes interval.

For this profiling I've configured JFR to record everything at maximum, all options enabled.

When I tried to dig deeper into the details by looking at the Method Profiling details, I observed that it seems to be related to org.apache.catalina.webresources.Cache.getResource().

So I started to read about Tomcat caching and tried out different parameters to tune it via the context.xml file like this:

<Context>
  <!-- Default set of monitored resources. If one of these changes, the    -->
  <!-- web application will be reloaded.                                   -->
  <WatchedResource>WEB-INF/web.xml</WatchedResource>
  <WatchedResource>WEB-INF/tomcat-web.xml</WatchedResource>
  <WatchedResource>${catalina.base}/conf/web.xml</WatchedResource>
  <!-- Uncomment this to disable session persistence across Tomcat restarts -->
  <!--
    <Manager pathname="" />
    -->
  <Resources cachingAllowed="true" cacheMaxSize="3024000" cacheObjectMaxSize="10240" cacheTtl="10000"/>
</Context>

In this particular example, which is the one used for the JFR profiling, I increased cache size to 3GB and cacheTtl to 10 seconds. I thought that a larger cache and larger TTL would effect the interval of the CPU spikes because I suspected Tomcat was checking the cache (originally 1G in size) every 5 seconds which is the default. However, whatever values I set for cache size or ttl, the periodical CPU spikes are identical. And the cache size is big enough to hold whatever Tomcat wants to put in there because I increased the value after we saw warnings in the logs. Anyways, 1GB is enough to get rid of the warnings.

I also experimented with heap sizes ranging from 1 to 5GB, the profiling above was done with a 5GB heap size. I can't really go above this value without starting to hit physical memory limits.

We use G1GC as our garbage collector since the Java 8 days. Tuning its parameters did not effect CPU usage. I also tried out ParallelGC and SerialGC but the CPU usage pattern remained unchanged.

Searching Google for this kind of issues lead to no results and I am totally stuck on what else could I try or what else should I look at.

Any suggestions are welcome. Thanks.

UPDATE 1:

It seems like I had a formatting issue originally, and the opening <context> tag was missing from the context.xml when parsed. Fixed it.

I also tried, as suggested with <Context reloadable="false"> so that reloadable is explicitly set to false. It had absolutely no effect.

Is it possible to set the reloadable flag from anywhere else? I am speculating maybe some other file or setting applies it even if in context.xml it is set to false.