Assertions starting after 4.2 -> 4.4 upgrade

Early this AM I upgraded the mongod data servers in our sharded (2 shards, 3 nodes each, no arbiter) cluster. I went from 4.2.18 to 4.4.18. I had done the config servers earlier this week without an issue. Since upgrading our monitoring system has been detecting an uptick in user assertions. I have been searching for a cause, and after setting the loglevel to 10 and grabbing a snippet from the logs, it appears that this is the error:

{"t":{"$date":"2022-12-08T10:37:52.164-06:00"},"s":"D1", "c":"-",        "id":23074,   "ctx":"conn5396","msg":"User assertion","attr":{"error":"CommandNotFound: no such command: 'shardVersion'","file":"src/mongo/db/service_entry_point_common.cpp","line":1362}}
{"t":{"$date":"2022-12-08T10:37:52.165-06:00"},"s":"D1", "c":"COMMAND",  "id":21966,   "ctx":"conn5396","msg":"Assertion while executing command","attr":{"command":"shardVersion","db":"drafts_recents","error":"CommandNotFound: no such command: 'shardVersion'"}}

This is happening on all 4 secondary shard servers, but not the primaries. The collections in these sharded dbs are still getting new documents, and replication appears to be working fine. I have not upgraded the mongos instances yet, those will be this weekend/next week to prevent impacts on production apps. Anyone know what might be causing this? Do I need to perform a roll-back?