I have no idea based on the above details (other than you are experiencing some kind of memory leak). After you attach the Eclipse Memory Analyzer Tool (MAT) to the WildFly application server process, you should see an initial pie chart that shows the memory usage. Take a screen shot of MAT and attach it here.
There are multiple articles about how to use MAT to find memory leaks. Doing a web search returned some below that you might find useful: