Store & Forward service unavailable and high mermory

We have purchased a set of modules for our development demand, including SQL Bridge,Tag Historian,Vision and so on. And the project has running for serval months.
Problem: I found that Store & Forward service unavailable this morning andbuffer error highmermory to gateway process. I operated the stop-ignition file to end the running process and then start the start-ignition file. After then, the process worked normally.
I’m confused about that.