No data is being received and the following errors appear when polling via an agent.
In this case, it is particularly about CONNECT permissions to individual databases. It affects a model database by default but this can be an issue as well for custom databases created by the user.
This means that during polling, all databases are read but some of them cannot be opened. Thus, data is not being received.
Performance counters specific to this database are being being polled without problems because they are read without the need to open the specific database. Total Size and Shrink Space are not real performance counters but they are calculated from the result of the above failing components so they are missing source data as well.