FluentPlayer Flicker with Captions

I’m seeing a small issue with captions in FluentPlayer when using a Gumlet-hosted video.

When captions are turned on, the entire video appears to darken slightly while a caption is displayed. In the brief gap between one caption line ending and the next one appearing, the video returns to normal brightness. Because of that, the video has a noticeable flicker throughout playback.

This only seems to happen with captions enabled. The brightness change affects the whole video frame, not just the black background behind the caption text.

Setup is FluentPlayer inside FluentCommunity, Gumlet video source, WebVTT captions, Firefox on macOS.

Has anyone else noticed this, or is there a setting/CSS rule that could be causing the player to dim while caption cues are active?