missing parens in LaTeX

Parentheses appear as expected in Ubuntu 16.04 but fail to appear in the latex math environment in Ubuntu 17.04. "$y=f(x)$" in the tex file should produce output that has parentheses around the x, but does not.

Seems to be a highly specific bug. The parens only go missing if using documentclass acmart (from the Association for Computing Machinery, available at https://www.ctan.org/pkg/acmart) and package sansmathfonts and Ubuntu Linux 17.04. Because it all works in Ubuntu 16.04, I think this is a regression in 17.04, and worth filing a report here. Was using acmart.cls version 1.25 on both systems. Updating acmart.cls to version 1.39 (the latest as of now) did not make any difference.