Is this a bug? Last seen 49707 days. 
RouterOS = 4.16
Nice.
(49 707 days 10 hours) plus (3 seconds) = 4 294 720 803 seconds
32 bit counter overflow. Send 'em a supout.rif, I guess, but the most likely cause in my opinion is that a DHCP timestamp got set and your clock adjusted, and that the delta between the future timestamp and the current time is adjusted as a wrap around.