When you activate the 'Agile 2.0 - Unified Backlog' plugin on GEITDev and GEITQA, sometimes but not often, errors related to the creation or modification of task records appear, for example:
Exception (TypeError: Cannot convert null to an object….on sc_req_item...
or a SQLException error referencing the agile_story field appears:

Syntax Error or Access Rule Violation detected by database (Unknown column 'task0.agile_story' in 'field list')

com.glide.db.GlideSQLException: FAILED TRYING TO EXECUTE ON CONNECTION glide.11 (connpid=167867): SELECT task0.`parent`…..)

Syntax Error or Access Rule Violation detected by database (Unknown column 'task0.agile_story' in 'field list')

The issue has yet to be reproduced on an out-of-box instance, and appears to be a timing issue on some customer instances. 
When an error appears, though, the tasks created or modified are not saved.

Madrid

The issue is related to the timing of cache flushes.
If the timing of the cache flushes is off, the error appears.  If you flush the cache, no more errors occur during the plugin activation.

The workaround is to manually flush the cache as soon as the 'Agile 2.0 - Unified Backlog plugin' is activated.

Here are the steps to manually flush the cache:
1) Go to Scripts - Background
2) In Scope global, enter this line in the 'Run Script' field:
GlideTableManager.invalidateTable("task");
3) Click 'Run script'.

Your instance will not experience a task record issue if you manually flush the cache as soon as the 'Agile 2.0 - Unified Backlog plugin' is activated.