I noticed (for example) that Spanish language shows have two cc streams. One in Spanish (the default) and one in English.
The Spanish one renders fine, but the English one has that weird garbling problem we used to see on some channels for English.
My Roku show the program as having ‘Track 1 of 2 (CC channel1)’ which is the Spanish captioning and ‘Track 2 of 2 (CC channel 3)’ is where the somewhat garbled English captioning resides.
Just an fyi @TabloSupport