Brightcove Connects breaks site after core upgrade to 8.5.x in Acquia Cloud
I discovered the issue. Case-sensitivity of the class names. Class "brightcove/src/Entity/BrightcovePlayer.php" extends "BrightcoveCmsEntity", while class "brightcove/src/Entity/BrightcoveCMSEntity.php" is named as "BrightcoveCMSEntity".

I replaced all instances of "BrightcoveCmsEntity" with "BrightcoveCMSEntity", and the issue was resolved, it exposed the same issue with "BrightcoveVideoPlaylistCmsEntity".

Fatal error: Class 'Drupal\brightcove\Entity\BrightcoveVideoPlaylistCmsEntity' not found in /mnt/www/html/nhradev/docroot/modules/contrib/brightcove/src/Entity/BrightcoveVideo.php on line 75

Replacing all instances of "BrightcoveVideoPlaylistCmsEntity" with "BrightcoveVideoPlaylistCMSEntity" resolved all issues.

The plugin now works as expected in Acquia Cloud.

NOTE, the code worked locally because I am developing on Windows.

Files touched:
brightcove/src/Entity/BrightcoveCMSEntity.php
brightcove/src/Entity/BrightcoveCustomField.php
brightcove/src/Entity/BrightcovePlayer.php
brightcove/src/Entity/BrightcoveVideoPlaylistCMSEntity.php

brightcove/src/Entity/BrightcovePlaylist.php
brightcove/src/Entity/BrightcoveVideo.php
brightcove/src/Entity/BrightcoveVideoPlaylistCMSEntity.php
brightcove/src/Form/BrightcoveVideoPlaylistForm.php

Reference: https://www.drupal.org/project/brightcove/issues/2969674