If you're still having this issue, please try resetting your BIOS to default. Be careful using this solution if you have made changes to your BIOS as you will need to make them again. Here is a helpful video for resetting the BIOS:      Marking as Dell Solution for visibility, please note there could be other reasons the system is getting this message but I wanted to provide a solution that has worked for some users. 
I have Dell Inspiron 15 5518 running Windows 10 On startup it started showing suddenly, Inspiron 15 5518"HTTPSBOOT Failed to initialize network connection" URL It doesn't boot now. I tried changing the boot sequence, but I can only see Uefi HTTPs Boot in my boot sequence, so there is no option of changing the sequence. How do I fix it? 
HTTPSBOOT Failed to initialize network connection