plot_fits_datasets_chi2 giving RuntimeError: libpng signaled error

Created by: wilsonmr

Just putting this here for record. I am comparing two fits (DIS baseline fits for th uncertainty) I noticed that the full comparison report was breaking. After some investigation I can see that the minimum vp runcard to get this error is:

use_cuts: "fromfit"

fits:
 - 190118-edi-mw
 - 181126-si-nlo-central_DISonly

theoryid: 163

actions_:
 - plot_fits_datasets_chi2

Actually I believe the error is at the level of reportengine and is thrown during https://github.com/NNPDF/reportengine/blob/2eec5f3986e6b2e80c7e3c039985b174a517fda5/src/reportengine/figure.py#L66 I have reproduced this error on both linux and mac installations, both for binary installation and from source. I think it is possibly linked to #302 (closed)