The following situation can happen:

1. The user has a sharded viewful timeseries collection "ts".
2. The user runs an aggregation, the router targets the shard with the view, so it triggers the view kickback mechanism (resolve sharded view on "system.buckets.ts").
3. "ts" gets upgraded to viewless format.
4. The router tries to resolve the view on "system.buckets.ts", since the config.collections entry for "system.buckets.ts" no longer exists, there's no routing info so it's re-routed as UNTRACKED.
5. The shard acquires "system.buckets.ts", since it's a non existing collection, UNTRACKED is the correct shard version --> Empty results

We should instead notice this either at the router or shard level, and re-resolve the aggregation from scratch.

A reproducer is attached.