@jmocallaghan,
If you're willing to continue to help the ZC community by identifying what issues were specifically generated, it would be much appreciated.
Using the software from github available at this link: https://github.com/mc12345678/Stock_By_Attributes_Combined and based on someone else reporting an issue with installing the software on ZC 1.5.4, I just completed two complete independent installations of ZC and the associated SBA software for each of the versions of ZC 1.5.4 (PHP 5.6) and ZC 1.5.5e (PHP 7.0.14) using the ZC demo product. In both cases, I had no errors generated... Not by SBA, not by anything else. I was able to add product to the admin database to be used to purchase as Stocked by Attributes, made purchases with items that did and did not have attributes, those that had attributes and were and were not tracked by SBA. Made those purchases individually as well as combined. I came across no issues with the products, available stock decreased as expected, items (variants) that were out-of-stock displayed such, etc...
So, while this all worked fine and dandy on my server, I'd be interested to know what led to issues on the installation at the server tested/used assuming you have any interest in seeing the software satisfactorily operate.
If you would please talk your way through the installation including any other software that is/was installed on the system, how the upgrade from ZC 1.5.5c to 1.5.5e was performed etc... PHP version, which fileset(s) were installed from the github version etc... I'm also working on instructions to publish the plugin and would appreciate further identifying areas of concern related to the installation for those that may have to go back to the instructions for further assistance. I have further documented this testing at the forum thread for SBA specifically at this post: https://www.zen-cart.com/showthread.php?47180-Stock-by-Attribute-v4-0-addon-for-v1-3-5-1-3-9&p=1329176#post1329176