Bug after add and remove product from compare table

Why sometimes when I add two products, open iframe compare table, clear it, and add the same product again and wasn’t add ? Ajax return 200, so I don’t know what is wrong.
Next problem is with products limit set in admin panel.
e.g
I add 4 product (this is my limit set in admin), and when i try to add another product there is no any information about this limit, no any information in woo hook, only when we run an iframe with a table, we see at the top that we have exceeded the product limit. It is’nt very good solution, because not everybody know that they can’t add more products. It should be display somewhere under button or in woo hook with informations`

https://imgur.com/a/F4e6Puz (ajax and loader after remove and add the same product again)