Hi Master-Sale ,
Thanks for your post.
If I understand you well, you are updating the purchase price and the stock levels from the Stock Central page. Am I right?
Are these fields updated when you enter the edit products page? If so, it means 'ysell.pro' is updating these quantities. I kindly suggest you contact them to ask why they are doing such a thing.
Please note that the purchase price is an ATUM field, and no third-party plugin should update it without any reason.
Anyway, please note that we don't support any third-party software apart from the plugins you can find here. If you need both plugins to work together maybe you'd need to find a good developer to assist you with the integrations.