Well seems like a bug, can be even from graphics card imo.
but also making credits as a long single umg can be anyway problematic imo and time consuming.
Why not use templating, especially if its a really long credits.
Like a CreditTextEntry that gets 1-4 Tmaps of title and name into a horizontal slot.
For CreditImageEntry that gets 1-4 Array of images with single title.
Get all entries even from a data table, insert , move and remove. Upon removal a new one is inserted etc. can be easier later on if there is new sponsor, special thanks etc.