JMeter load get decreasing after a long duration test

Recently, I did a long duration test with a consistent load to the server to see how stable of our application is.

our application survival after almost 12 hours torment，but seems JMeter can not generate the consistent load(load get decreasing a lot) after about 5 hours or so, I do not know what happened to either our application or JMeter....

i just restart the JMeter only, so the load get back to normal again, it should be some problem on JMeter side:

BTW, I just add the aggregate report listener only during long duration testing, and no other logs output.

Have anyone met this problem before? someone found aggregate report will get the load down due to increasing calculation of 90% line.