[P.J.]

If you read the section of the tournament rules that deals with field faults, the blue box underneath it reads:

Note that an ARENA FAULT that does not affect MATCH outcome
in the judgement of the Head REFEREE does not lead to a MATCH
replay. Examples include, but are not limited to:
A. a piece of FIELD plastic falls into the FIELD in the last 5 seconds of a
MATCH, far away from any human or ROBOT activity, and in such a
way that it does not affect MATCH outcome
B. delay in the playing of an ARENA sound
C. mismatch between the timer on the Audience Screen and the FIELD
Timer

While it was in the last ~20 as opposed to 5 seconds, it would appear this piece of field plastic broke off and fell into the field and did not affect the match outcome. If you watch carefully 1477 gets stuck on boulders, not the actual field piece. So it was within the rights of the Head Referee to choose not to replay this match.