i know you have made it already but you shouldnt run multiple workflows for a given task like yours!
why? workflows are system hogs, your creating multiple workflows that run every day and will over time slow your system down due to huge workflow lists and workflow processes. Workflows are ment to be one offs... what your doing is repeated on a daily basis with a workflow that activates another workflow.. that is constantly running.
A better solution would be to make a timer job, Job would run every day after 12am, say 12:15am - 01:15am. This will pickup any review dates for that day and email out to user.... that can be done by looping through each item or run a query to return specific items.
somthing similar to this:
either solution is labour intensive and should be run out of hours to minimise slowing servers down.
as for your initial issue, i cant see what code you made for your workflow to sugest any solution.
issue could be related to appending the text which is turned on and could be setting blank text:
to use "Append Changes to Existing Text" you need versioning enabled on the list:
If you’ve selected Yes, the key thing to note is that SharePoint will
store blank entries in the Version History of that item. If this
option is set to No, SharePoint will still record any updates to the
field as versions of the item, but it won’t store any blank entries.
This is an important consideration if you’re building any custom forms
or views for this data and are worried about blank entries showing up.