pmm server got high iowait

my english is poor,forgive me
my pmm server hardware info:
16cpu 64G mem
Last Saturday and today I suddenly received a lot of warning emails like NO DATA . seems like that pmm can’t get data. so i login to the server and use top iostat iotop . i found that the io load is high ,see the pic,
can anyone explain why?

Have the same situation. Suddenly iowait grew up yesterday and still at the same high level.

i forgot to say my pmm version is 1.3.0