Since 21w10a, titles with fadeIn or fadeOut appear/disappear before the fade is complete, leaving a noticeable cut in the transition.
How to reproduce
Run the following commands in order:
/title @a times 100 100 100
/title @a title {"text":"_______"}/title @a times 100 100 100
/title @a title {"text":"_______"}If these commands are executed in a version later than 21w8b, you will notice that the title appears and disappears a bit before finishing or starting its transition.
Comparison:
[media]
This is probably caused by the render text shaders, which detect if the alpha (transparency) value is lower than 0.1 to discard the render, causing all text with alpha between 0.0 and 0.09 to not display. This can be easily fixed by removing that check from those shader files.