Replied 17 April 2019, 8:44 pm EST
OK, i've gotten to the bottom of why the text doesnt appear when exporting. Its because i have the reference to wijmo.chart.render.js included. If I remove that, then it exports in Chrome just fine, including the text drawn with engine.drawString.
The problem is that it is needed under IE otherwise I get a "security error" message. However, under IE it still does not render the text drawn with engine.drawString. You should be able to replicate this issue by including the render JS file in your sample and running it under IE or Chrome.
I do not know if the issue I reported above whereby all the pie charts update their text magically when exporting a single chart will now be fixed, so I'm going to test that out and report back.
I have a real sense of deja vu with this, as I'm almost certain that I discovered the exact same issue using wijmo 3 charts, now I come to think about it.