  The compact mm-wavelength signal in the central cavity of the PDS70 disc,
revealed by deep ALMA observations, is aligned with unresolved Halpha emission,
and is thought to stem from a circum-planetary disc (CPD) around PDS70c. We
revisit the available ALMA data on PDS70c with alternative imaging strategies,
and with special attention to uncertainties and to the impact of the so-called
"JvM correction", which is thought to improve the dynamic range of restored
images. We also propose a procedure for the alignment and joint imaging of
multi-epoch visibility data. We find that the JvM correction exaggerates the
peak signal-to-noise of the data, by up to a factor of 10. In the case of
PDS70, we recover the detection of PDS70c from the July 2019 data, but only at
8sigma. However, its non-detection in Dec. 2017 suggests that PDS70c is
variable by at least 42%+-13% over a 1.75yr time-span, so similar to models of
the Halpha variability. We also pick up fine structure in the inner disc, such
that its peak is offset by ~ 0.04" from the disc centre. The inner disc is
variable too, which we tentatively ascribe to Keplerian rotation as well as
intrinsic morphological changes.
