Might be because the test is already finalized by the time a screenshot is taken. Are you sure it worked in 4.0.0? Any chance you can provide a reproducible test case? That would greatly speed up the resolution.
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Please try taking regular screenshot (from the normal test flow, not on the error). Does that work?
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Hm.. What if you copy the files in /bin/binary/imagemagick
from 4.0.0 to 5.5.1? Will it work after that?
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