Looks like the blank cracked.
Did you perhaps turn this using excessive pressure on the ends of the blank, or assemble it with too much force ?
I've had similar problems with both !
What often appears to be a tight joint at 1" OD may not be so tight at the final OD of the pen (e.g .462"). It may have separated during drilling/turning, etc, but I suspect the joint was not perfect when glued-up. (Just speculating now, and I may be totally incorrect).
There is a slight "wave" with the chevron joint, and this also may indicate not a perfect match for the sections.
I have a plastic tub with 40-50 "if only except..." blanks.
And yes, what you assembled looks mighty nice.