1: What does the log message is referring to?
The problem is caused by Tomcat being unable to reach its target cache size due to cache entries that are less than the TTL of those entries. As Tomcat didn't have enough cache entries that it could expire, because the entries in cache are afresh, it couldn't free enough cache and thus outputs warnings.
The problem didn't appear in Tomcat 7 because Tomcat 7 simply didn't output warnings in this situation. With upgrade of Tomcat to version 8 CARA started to log this message as we are using the default cache size.
2: How can the error be normalize or can be subside?
The maximum of static resource cache (all resources in total) is by default 10240 kbyte (10 mbyte). The cache size can be increased from default value by adding following line to the RA_HOME\conf\context.xml file, at end of the file just before the </Context>
<Resources cachingAllowed="true" cacheMaxSize="100000" />
# This will increase the cache size to 100Mb.
You need to restart the Release automation Tomcat service.