Prblem with bandwith balancing

hi i have a MT with 2 Internet conection and 1 conecction to my network

some times i when i check the traffic i get intervals of inactivity in the eth ports…
like show in the picture…

some of this holes are 4 sec

some one can help m i telme what can produce this problem.
error mikrotik.JPG

login by IP not MAC
also update to actual version 3.14