I doubt this is something recent, as from Seaside 3.0 WARenderCanvas should be replaced by WAHTMLCanvas, and in Seaside 3.1 WARenderCanvas is no longer there.
So thank you for your bug report: Stephan and I are currently fixing this and replacing all references to WARenderCanvas by WAHTMLCanvas. This appeared not only a Pier issue, but even a Seaside 3.1 issue (only in comments, but still).
Has anyone noticed that the images from https://ci.inria.fr/pharo-contribution/job/Pier3Addons/PHARO=30,VERSION=stable,VM=vm/
are having issues with the editor? When one tries to open it, it gives the loading message in the text area, a few inactive links, and the message
MessageNotUnderstood: receiver of "builder" is nil
I'm getting this from a Pharo 3 VM and testing the files from Mar-7th until today's image. At first I thought this may be due to WARenderCanvas being undefined, but I've found an image from a month ago that works fine. Anyone know the last time this worked successfully?
Magritte, Pier and Related Tools ...