ACARS
There seems to be general perception here that ACARS transmissions are more or less continuous - that is NOT the case.
Each ACARS message cost money - not much - but if an aircraft is sending out continuous messages it adds up really fast. Hence, ACARS is set up to transmit only when specific events occur - e.g. a system or LRU reports a fault. Similarly, engine condition monitoring does not continuously spout out data via ACARS or other downlink. Rather there are engine parameter algorithms that look for certain 'stabilized' events - e.g. stabilized takeoff or cruise conditions. If those specific events are not met, nothing is downlinked.
So, the absence of apparent ACARS messages is not in and of itself unusual. What is potentially of interest is that the lack of ACARS messages would either imply either a lack of systems failures or a sudden failure (or human action) that disabled ACARS.