I've had a similar problem. It seemed that if certain data points were enabled, everything from that device would read "Point value may not be reliable." The problem seemed to go away for the remaining data points if those "problem data points" were disabled.
After some experimenting, the problem went away entirely if the following boxes were selected in the data source menu:
- “Use multiple write commands only”
- “Contiguous batches only”
- “Create slave monitor points”