There is a major performance drop after 4.18 when calling draw material to render target. This is an issue reported by many community members, and there seem to be additional reports with different repros. Below is a link to the forum post where the community discussion is taking place and a JIRA that is related but caused by a different issue.
Working properly in 4.18 CL# 3832480
Found in 4.19 CL# 4033788, 4.20 Preview 3 CL# 4135216, 4.21 CL# 4136834
This is a regression.
Performance is very poor in comparison to 4.18
When playing in standalone the performance should match
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-60787 in the post.