Frontend Developer for Website Issue

In the last week, we had several reports of clients being unable to access our application, and now I am also able to replicate the issue on all environments (development, staging, and production). When loading the application, on each page change (or endpoint), this error attached occurs. But when the page is refreshed, the application loads correctly. Rinse and repeat. It is intermittent on Chrome and always happening on Edge. I am not a strong frontend developer, so I am looking for someone who is confident in frontend code (React) A huge client is onboarding Monday, so ideally it will be resolved before the weekend is over.