You may be correct there's no issue with the XML file. As I said, I have no experience with applying them in BIAB/RB or knowledge of using them in any manner. Also, XML files ability to be imported into PGMusic software is a fairly new feature so I was giving my best guess. Your issue with the two instances of INTERLUDE also led me in this direction. At the same time, I'm fairly confident from the various results obtained, there's no defect with RealBand regarding generations of 240 or 255 bars.

It sounds odd when I say it but I believe the issue is no more than something from somewhere has put a command around bar 240-241 since you consistently have the issue there.

You can easily select a few bars prior to bar 240 carrying the selection beyond 241 perhaps to bar 245 and manually make changes to the chords, replace instruments and only regenerate those few bars to see if completing a smaller size task makes a difference. You can do this to one instrument or to all of them at that section only.

To select a section of all the instruments -

Select the radio Snap To Grid Button in the upper left tool bar area.

Select a track, multiple tracks or all the tracks (to select multiple tracks use the control on any desired additional track or shift key between the first and last track you want to choose.)

Place your curser at bar 238 and Press F7

Place your curser at bar 245 and Press F8

The selected section (all tracks)should be highlighted in blue.

Right Click on the blue selected area or Select the large Generate Button

From the drop down menu - Generate\Regenerate All (selected region) (selected tracks) - The selection reads different in the large radio generate button than from the Right click method but the result should be the same.

Only the selected area should regenerate and apply the changes you made to the chord chart.
BIAB Ultra Pak+ 2022:RB 2022, Latest builds: Dell Optiplex 7040 Desktop; Windows-10-64 bit, Intel Core i7-6700 3.4GHz CPU and 16 GB Ram Memory.