Hi, I use the pro version recently with a letter suffix for variation. But some time it’s work and many time not. The variant sku are the same as the product without the letter suffix on a majority of product.. I don’t have other plugin activated for sku.
Are you using SKU tool to add SKUs for existing products, or are you adding SKU automatically, when adding new product? If it’s the latter – you should enable “Delay SKU generation till product is published” checkbox in plugin settings, so SKU won’t be added too early, when variations are not yet created.