Broken TTML subtitles with v3.1.3

Created by: Robloche

Environment

• The MPD passes the DASH-IF Conformance Tool on https://conformance.dashif.org/
• The stream has correct Access-Control-Allow-Origin headers (CORS)
• There are no network errors such as 404s in the browser console when trying to play the stream
• The issue observed is not mentioned on https://github.com/Dash-Industry-Forum/dash.js/wiki/FAQ
• The issue occurs in the latest reference client on http://reference.dashif.org/dash.js/ and not just on my page

• Link to playable MPD file: Unvailable because DRM-protected
• Dash.js version: 3.1.1
• Browser name/version: Chrome 85.0.4183.121 (Build officiel) (64 bits)
• OS name/version: Windows 10

My subtitles were correctly displayed until version 2.9.3. Then, from version 3.0.0 to version 3.1.1, they weren't displayed at all. In version 3.1.2, they were back and working. But now, with version 3.1.3, they're broken again (but not in the same way as before), as you can see below:

Here's what happens in the console:

Here's an example of subtitles: subs.zip