unable to retrieve function in Azure Function APP

The problem "internal host error" appears every time I attempt to build a function (HTTP Trigger) in a Function APP. However, after several attempts, I was able to successfully create the function. After writing the function and testing, I exit the page, but upon returning to the same function, I continually receive the message "error retrieving the function." Eventually, I am unable to locate the function at all because it has been automatically deleted.