I am sort of baffled as to how anything is working with that version of SLP. You have Premier subscription which means you have Power, add-on available to download which replaced ProPack and Tagalong quite a while ago. Are you keeping those alive because of your PHP version? we no longer support either of those plugins.
SLP is on version 5.0.3, etc etc. (see updating and where to find0 We have not supported proPack since WP version 4.8 and SLP version 4.8.2. WordPress auto updated everyone to version 4.9.9 as you are showing. WP version 4.9.9 broke the ability to import csv. See the developers post here
They fixed the bug that they introduced with WP version 5.0.3 .
Make sure before you update or do anything you have a site backup.