'Server error after opening many browser cards

I've a Vue app in production. There are 11 products subpages. When i'm opening all of them in new cards then on two of them i'm getting error like on screen. After that i'm getting this error when i'm trying to get on url, but when i try to open this subpage vie the menu, everything works normally. Error disappears after at least 15 mins.

The app is deployed on Hetzner VPS.

That's the nginx error log.

2022/04/29 09:39:30 [error] 28297#28297: *102057 connect() failed (111: Connection refused) while connecting to upstream, client: 188.121.2.106, server: www.oknar.pl, request: "GET /api/translations?path=forms.contactForm HTTP/2.0", upstream: "http://[::1]:8083/api/translations?path=forms.contactForm", host: "www.oknar.pl", referrer: "https://www.oknar.pl/realizacje"

Error screen



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