I noticed that the new built-in filter in Studio (Subtitle formats - Subtitles v184.108.40.206) has trouble processing SRT file if the file extension is in capital letters.
I tested with a copy of the same file, one with .srt extension and the other with .SRT. The first one is processed correctly, while the latter is empty.
It doesn't happen with the external filter (SRT v220.127.116.11)
I didn't check mixed case and only tested on SRT format.