Because you completely overloaded you computer with your specific settings:
Code:
17:55:40.438: Output 'simple_file_output': stopping
17:55:40.438: Output 'simple_file_output': Total frames output: 189049
17:55:40.438: Output 'simple_file_output': Total drawn frames: 661659 (1190801 attempted)
17:55:40.438: Output 'simple_file_output': Number of lagged frames due to rendering lag/stalls: 529142 (44.4%)
17:55:40.482: ==== Recording Stop ================================================
17:55:40.489: Video stopped, number of skipped frames due to encoding lag: 189000/189074 (100.0%)
Your CPU simply isn't strong enough to encode 4k output resolution. Use Tools->Auto Configuration Wizard to get a working baseline configuration.