Hello Aquaaa,
Just to clarify – the url of any item post is (using your example and supposing the the Permalinks are set to show pretty urls)
Item post title is ABC
https://domainname.com/a3-portfolio/ABC
when the item card shows on the Portfolio page with all the other items the portfolio url would be
https://domainname.com/portfolios/ or whatever it is that you call the portfortfolio – but we will stick with the result
Each time an item card is clicked to open the expander an identifying extension is added – example if the ABC item card is the 6th card on the portfolio when it is clicked to open the expander – the page does not reload because this url is generated
https://domainname.com/portfolio/#item-6
and this is what you are referring to – go to the next item a and it will show /#item-7/ previous /#item-5 and so on.
You can use the https://domainname.com/portfolio/#item-6 to direct people to the item on the portfolio and if no items have been added or deleted the page will load and #item-6 expander will open. If items have been added or deleted #item-6 will open but it will not be the item that was there before.
It would be much better to post the link to the actual item post eg https://domainname.com/a3-portfolio/ABC
We could add a setting that would allow admin to change the word item in #item-6 extension – but that would apply to all items – even if it was dynamic and could show the post name eg /#ABC-6 the number at the end is the location identifier within the portfolio items – so as soon as another item is added to the portfolio that url extension would become /#ABC-7 and any link that was posted when the item was the 6th item would not land the user on that open expander item within the portfolio – but instead give a 404 error because item 6 would have another name.
Hope all of that information helps you understand why item expander extension url is displayed the way it is. Steve