Just tested(via ProtonVPN) ROS 7.11.0 Stable on RB750GL and IPsec correctly working without intermediate certificate, although I don’t see direct mention of resolving this problem in release changelog >_>
Upd.
If you are still getting an error after upgrade, then remove the root certificate, re-import, and correct tunnels configurations where this certificate was used.
I had such problem on one of my devices(RB4011) and the described workaround helped.