With version 2.1.2, the following causes cypari2 to allocate memory at several GB per minute:

>>> import cypari2
>>> pari = cypari2.pari_instance.Pari()
>>> while True:
...     M = pari.matrix(10, 10, range(100))

Observed in Python 3.8 and 3.9 as part of SageMath 9.3-9.5 on both linux (gcc) and macOS (clang).

For what it's worth, the other cypari does not seem to have this problem.

Also filed at the SageMath trac.