I understand that this is an old question, but when I ran into problems with the long-term use of Monolog using a script that generated errors in memory, it turned out that the problem was handled by Monolog's finger_crossed handler, the log messages.
I solved the problem by setting the buffer_size variable for the Monolog handler in question. Something like that:
main:
type: fingers_crossed
action_level: info
buffer_size: 200
handler: nested
: , buffer_size : " , , ".