I think the fact that a service to Gloucester needed to be switched at Bristol from a 165 to a 158, so they involved two units for one working is odd.
But the fact that swap happened whilst passengers were on it, rather than wait until empty rather suggests they are overstretching themselves even if it inconveniences passengers.
The 158 it was swapped with came off 2K26 (Weston Super Mare to Severn Beach), which the 165 swapped on to. Are 158s cleared to Severn Beach, if not this might explain, as swapping meant both services could run.
As for swapping at Bristol, this is just a side effect of where the depot is. A lot of diagrams are only empty at places like Gloucester, Southampton and Weymouth. It doesn’t make sense to send a unit empty on a 2 hour trek when you can swap it at Bristol for minor inconvenience of a same platform change.
But I didn't explain myself well, it was the number of 2car units operating singly on very long services, rather than 3car units that I thought was odd.
The fleet is too stretched to strengthen diagrams. That they ran at booked length if nearly an achievement at the moment. To run them as 3 cars they would’ve had to short form another service, which they will earn a performance penalty from.
Doesn't bode well for a fleet they have to maintain until 2028, and which needs to operate the expanded Metrowest service from next month that GWR are unable to find enough serviceable units to operate current timetable.
I agree this is worrying, although today they are almost together, with I believe only one short formed diagram on Cardiff to Portsmouth. As for MetroWest this is being achieved by splitting some 3 car 158s into 2 cars, and replacing a diagram with an IET. Overall they should have about the same amount of difficulty as now, which isn’t great but not a disaster.