The first thing you should do is look through our guide on fixing syncing issues. Many of the most common problems can be resolved by following those steps.
Syncing Product and Collection single pages may take up to 5 minutes depending on the size of your Shopify store and speed of your WordPress site. If you have over 1000 products you can expect the sync to take around 5-10 minutes.
Under the plugin settings, you can try changing the “Items per Request” option to 25, and turn on “Synchronous Requests”. After these are updated try re-syncing again.
Also, take a look at our syncing tutorial video.