My experience is that ~50 pax is usual for the route, and there's usually one or two in business. Once or twice the flight has been full (overbooked, even), so I guess the cost saving on using a CRJ isn't substantial enough to justify it being the norm.
The two things that are concerning me:
* No LH4964 from FRA-BRS on Friday evening - that's really going to make it difficult to do any work in Europe on a Friday. (I don't mind the loss of the mid-day rotation, which I suspect exists mainly to catapult a crew in for the following day's first flight).
* No flights to FRA at the weekend. That's going to hit my leisure travel a fair bit. If they do put in a Friday evening flight FRA-BRS, it makes sense to send it back as LH4961 min-morning on Saturday (which allows the same crew to work it back as came out on Friday night).
I've written to LH asking if they'll look again at these two issues, and fingers crossed...
Obviously, the other explanation is that the crew have been down to the Centre in Bristol on a Saturday night, and no longer want to be anywhere near the place at the weekend....