Why has China put building two aircraft carriers on hold?
China will not put this project on hold. Evaluate your info source. Otherwise you will believe the nuke explosion in SCS not long ago.
China adopts Deploy + Build/test + Design in military technology development cycle.
When one generation is deployed, the next generation is being built and test, further generation is being designed.
Since aircraft carrier is new to China, deployment of first generation took longer for pilot training and collecting data from 001 testing. Chinese pilots have already been training overseas to get ready for aircraft carrier pilots years ago. A 1:1 live size aircraft carrier model has been build on land for training purpose as well.
Thus, China puts on hold aircraft carriers project is fake news.