its a wholesaler page
This would be for me an explaination for such ups and downs.
Firstly, not all items are unique - so Google needs time to get this.
Secondly, i suppose, that you have a high volaitility on your site - means, products are published and sold out very fast.
Indexing is a sluggish process - it happens very often, that just after your product was indexed, is it already sold out and Google tries to get the up-to-date status through deindexing of soldout products again.
This setup is nothing dangerous. But it isn't optimal regarding of usage of Google's ressources. Try to index only those products, which are always on sale. Another good way could be to index product categories.