A client organisation (and I imagine many, many other people) are running on version 2019 of Reader.
Unfortunately v2019 has display issues and can add what look like black or yellow felt tip dots and lines at areas where effects overlap.
They are not seen in Pro or in v2020 or in v2015 of Reader. Just v2019. So what we see in our pdfs, is not what our clients or their audience might be seeing. So every user of Adobe CC is exposed. Our work might not look the way we intend if a viewer is using v2019of Reader. And I can imagine that is most people. So as a design community and Adobe CC client base, we can't be confident that our work is being seen without problems ... which damages our credibility and leads to exasperating conversations because we don't see the issues our clients are asking us to correct.
We as a design community need to know about the issue so that we can at least know about if a client request doesn't make sense.
Bit it also means that our work might be viewed in a way that looks unprofessional and messy and it's because of something beyond our control – a version of reader with a glitch.
Using version 2020 seems to have cleared THIS issue up.