Personal temple ordinance reservation lists in FamilySearch now have a maximum of 300 rows of reservations per user. This update is to encourage members to not reserve more names than they can realistically get done.
Read more in the Church News article “FamilySearch announces 300 limit for personal temple ordinance reservations. Here’s why,” which includes questions and answers.
Note: If you try to share your extra reservations with the temple, please note the following: If those reservations came from the “shared with the temple,” you cannot share them back, but you will need to un-reserve them.