To clarify: The change is at P+ - not SF
The Agency.s01e01
<AdaptationSet id="20" contentType="text" lang="en-US" subsegmentAlignment="true">
<Role schemeIdUri="urn:mpeg:dash:role:2011" value="forced-subtitle"/>
<Representation id="39" bandwidth="3" mimeType="text/vtt">
<BaseURL>en-US_fn.vtt</BaseURL>
The Agency.s02e01
<AdaptationSet id="18" contentType="text" lang="en-US" segmentAlignment="true">
<Role schemeIdUri="urn:mpeg:dash:role:2011" value="forced-subtitle"/>
<Representation id="23" bandwidth="879" codecs="wvtt" mimeType="application/mp4">
<SegmentTemplate timescale="1000" initialization="PPPAR_THEAGENCY_201_UHD_V1_en-US_fn/vtt_init.m4v"
Result with mp4 + srt
[DC.Base] "SP: level: 3, message: [ttml_parser.cpp:37] [subtitle_processor::core::parsers::TTMLParser::parseString] TTMLParser::parseString - Invalid TTML structure"
[DC.Base] "SP: level: 3, message: [SubtitleProcessor.cpp:347] [subtitle::SubtitleProcessor::Impl::createErrorResult] Failed to parse subtitle content"