Python code will drop frames

I am using cyclonedds c and python, using version 0.10.5. I am running a publisher on PC1, publishing a message every 1.2ms, with a counter. I am running 2 demos on PC2, implemented in c and python respectively. The C demo prints out continuously, but the python demo prints out a difference of 16~18 between two consecutive counts every 1-2 minutes, which looks like frame loss.