I tried this again today, and now it magically works.
pd-san2::*> statistics show-periodic
pd-san2: cluster.cluster: 10/22/2021 17:25:57
cpu cpu total fcache total total data data data cluster cluster cluster disk disk pkts pkts
avg busy ops nfs-ops cifs-ops ops recv sent busy recv sent busy recv sent read write recv sent
---- ---- -------- -------- -------- -------- -------- -------- ---- -------- -------- ------- -------- -------- -------- -------- -------- --------
0% 1% 13 13 0 0 71.5KB 17.9KB 0% 52.7KB 2.25KB 0% 15.9KB 15.5KB 3.98KB 825KB 218 131
1% 2% 7 7 0 0 294KB 246KB 0% 47.2KB 2.16KB 0% 244KB 244KB 3.69MB 3.23MB 233 156
0% 1% 0 0 0 0 45.7KB 39.2KB 0% 3.03KB 65B 0% 40.0KB 39.1KB 11.9KB 0B 267 200
I dunno. Maybe the filer was having a bad day earlier