Fix deadlocked engine in RPC #1439

Job	Run time
Build (x86_64-pc-windows-msvc)	8m 33s
Build (aarch64-pc-windows-msvc)	8m 2s
Build (x86_64-apple-darwin)	8m 6s
Build (aarch64-apple-darwin)	8m 8s
Build (aarch64-apple-ios)	7m 30s
Build (aarch64-apple-ios-sim)	8m 14s
Build (x86_64-unknown-linux-gnu)	3m 50s
Build (aarch64-unknown-linux-gnu)	5m 58s
Build (aarch64-linux-android)	4m 11s
Build (armv7-linux-androideabi)	3m 54s
Build (x86_64-linux-android)	3m 42s
	1h 10m 8s

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