How to reproduce:
1. Open the attached project "1284053.zip"
2. Double-click "New VFX" in the Assets folder
3. In opened VFX graph find Update Particle Node's (on the left) -> Trigger Event Always -> Evt
4. Try connecting it to "New VFX_Subgraph" node
5. Observe console
6. Try connecting it to "GPUEvent" that's connected to "New VFX_Subgraph_Alt"
7. Observe console
Optional
8. Try connecting it to "GPUEvent" that's connected to "Initialize Particle"
9. Observe Game View while having "SampleScene" opened

Expected results: No console errors are observed and VFX works as intended
Actual results: Console errors are observed:
(Compute shader ([System 1]Update Particle): Property (eventListOut_a) at kernel index (0) is not set, New VFX : Exception while compiling expression graph: System.NullReferenceException: Object reference not set to an instance of an object)

Reproducible with: 8.2.0 (2020.1.9f1), 10.0.0-preview.27 (2020.2.0b7, 2021.1.0a5), 10.1.0 (2021.1.0a5)
Couldn't test: 2018.4 and 2019.4 as lacking VFX functionality, other console errors

Note:
Optional steps are for observing that VFX is indeed working