Not working page with query params

Hi, guys! Could anybody help, please? I have a Backstage page on my site, its link is “mysite/bstage” .
There are 2 tabs with the terms of custom tax “backstage”: “Diaries” and “Episodes”, their code looks like:

/*first tab*/
<a class="link active" href="https://projectdmc.org/support/topic/not-working-page-with-query-params/mysite/bstage?term=Diaries&amp;id=67">Diaries</a>

/*second tab*/
<a class="link" href="mysite/bstage?term=Episodes&amp;id=71">Episodes</a>

When I click a tab, the page reloads, the link “mysite/bstage?term=Diaries&id=67” (for example) appears in the address bar, the tab becomes active and WP loop outputs its posts – everything’s works fine.

But when I enter the page for the first time, there are no query params in the page link yet so there are no posts below the tabs. I tried to add “?term=Diaries&id=67” manually to the page link (with WP functions in functions.php or with the slug field when editing the page in the admin bar), WP forms the link with query params as desired, but for unknown reason the page is not loaded (not found 404),

i.e. if I click the tab and it makes the page reload, forms the desired link with “?term=Diaries&id=67”, I get what I want. If I add the same params with the code so that the Backstage page opens straightaway with the first tab active and its posts below, I get 404 page not found… How can I fix this?