You say, "What is odd is that this exact code "used" to work every time"

Have you updated ESP or other supporting software in the mean time? If so, can you go back to the earlier software to see if anything has changed?

I had some network issues that were relieved by preventing the ESP WiFi ...

I am working on a project that requires sending large files, .png, css, javascript, etc. from an ESP32 server to a client browser.

I extract the file content as bytes, store it as constant arrays in flash, and simply use the constant array as the data source in the server's send command, no RAM ...