Fix deadlocked engine in RPC #1429

Job	Run time
Build (x86_64-pc-windows-msvc)	7m 52s
Build (aarch64-pc-windows-msvc)	8m 2s
Build (x86_64-apple-darwin)	5m 41s
Build (aarch64-apple-darwin)	9m 18s
Build (aarch64-apple-ios)	10m 3s
Build (aarch64-apple-ios-sim)	6m 16s
Build (x86_64-unknown-linux-gnu)	4m 12s
Build (aarch64-unknown-linux-gnu)	5m 48s
Build (aarch64-linux-android)	3m 31s
Build (armv7-linux-androideabi)	3m 40s
Build (x86_64-linux-android)	3m 49s
	1h 8m 12s

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