I can reproduce this in Chrome 69 as well (high-end Desktop PC). Judging based on my performance profile, GC is all out again and doing its thing whenever it likes to, this time it seems to trigger whenever Construct performs runtime work with draw calls in it.
Speculation Alert: This might be caused by objects being destroyed or created.
I'd do a Chromium bug report but this example is a bit too unreliable for me. Currently trying to figure an example which triggers GC calls by doing the things mentioned above.
If anyone's got suggestions or a more reliable example, please post it here and I'll check it out.
Found this reported bug, which might be related?
https://bugs.chromium.org/p/chromium/issues/detail?id=815259
This happens across browsers though, more or less.
Nah that's something else, nothing to do with this issue.