Running the following once increases updateArrayFilters by 2 in serverStatus.metrics.update:

{
	"update" : "testColl",
	"updates" : [
		{
			"q" : {
				"_id" : 1,
				"timestamp" : ISODate("2021-05-18T00:00:00Z")
			},
			"u" : {
				"$set" : {
					"a.$[i].b" : 7
				}
			},
			"arrayFilters" : [
				{
					"i.b" : 6
				}
			]
		}
	],
	"writeConcern" : {
		"w" : "majority"
	},
	"lsid" : {
		"id" : UUID("7c4f9933-4a2a-4716-b6b8-f8e42fee6b3a")
	},
	"txnNumber" : NumberLong(11)
}

I think it is because this code means we go into this twice.

Maybe the incrementUpdateMetrics loop should be in a if(!isTimeseriesViewRequest || !opCtx->isRetryableWrite() || !opCtx->inMultiDocumentTransaction()) or similar ?

I added a TODO for this in a bulk_write js test comparing those metrics between bulkWrite and non-bulkWrite.