EBU subtitles regression in 4.1.3 - subtitles lost: not added to region

[david-hm-morgan]

Have you read the FAQ and checked for duplicate open issues?
Yes

What link can we use to reproduce this?
https://shaka-player-demo.appspot.com/demo/#audiolang=en;textlang=en;uilang=en;asset=https://otvplayer.nagra.com/vod/dash/clear/bbc/bbc_ebu-tt-d_subtitle_fragmented/dash/ondemand/elephants_dream/1/client_manifest-all-minus-1080p.mpd;panel=CUSTOM%20CONTENT;build=uncompiled

What version of Shaka Player are you using?
v4.3.0-uncompiled
and all the way back to v4.1.3-uncompiled

What browser and OS are you using?
Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36

What did you do?

1. Play this stream with captions enabled
2. Observe the captions at 2:52 to 2:57

What did you expect to happen?
See the captions as follows:
You have to learn to listen.
then
This is not some game.

i.e. from the following TTML snippet.

...
            <p begin="00:02:52.00" end="00:02:54.80" xml:id="sub23">
                <span style="s1">You have to learn to listen.</span>
            </p>
            <p begin="00:02:55.84" end="00:02:57.64" xml:id="sub24">
                <span style="s1">This is not some game.</span>
            </p>
...

What actually happened?

Neither of these were shown, nothing was in this time range.

Note: this can only be reprod by playing the stream through this range uninterrupted, if you pause in that region, they can be shown without issue.

Note: I believe this was introduced in #4412

Note the coincidental relationship with #4631 on the same stream and same release.

[joeyparrish]

I see you're using v4.1.3. Please try the latest release in that branch (v4.1.7) and overall (v4.2.4 as of now, though v4.3.0 will be out later today).

(We ask similar questions in the issue template, but you seem to have deleted them. Filling out the issue template saves a lot of time for everyone involved, especially across many timezones.)

If you're still seeing the issue in those more recent versions, that would be useful to know. Thanks!

[david-hm-morgan]

I see you're using v4.1.3. Please try the latest release in that branch (v4.1.7) and overall (v4.2.4 as of now, though v4.3.0 will be out later today).

(We ask similar questions in the issue template, but you seem to have deleted them. Filling out the issue template saves a lot of time for everyone involved, especially across many timezones.)

If you're still seeing the issue in those more recent versions, that would be useful to know. Thanks!

Sorry, I cloned the similar issue rather than started afresh from the template and lost some stuff. Refreshed now with the template.

Confirmed still present in 4.3.0.

[david-hm-morgan]

After some time of debugging this, some clues emerging.
Just before the cue (say N) that is not shown, the region element is uprooted when we remove the cue N-1.
Then it is not reinstated when N or N+1 is handled.
Only reinstated with N+2.