I have the exact same problem with my Dell U2413. It is just 26 months old as of 4/Jun/2018. It started happening 2 weeks prior to that date. I think it is an issue with this model because I'm running it as part of a dual monitor setup and the 11 year old Dell 2007WFP is fine. Both are connected to the same graphics card (NVIDIA GTX 970) in a very high spec Chillblast photo editing computer. I have 2 other Dell monitors over 10 years old and they are still working very well (both connected to Dell computers BTW).
Started your own thread. Turn the PC and both monitors off. Disconnect the 2007WFP and all of its cabling from the PC. Test only the U2413 on the PC. Send me via Private Message = U2413 Service Tag number U2413 20 digit S/N U2413 A0x revision