How to restart chain attack stream during a single stun? No astra, no Eve

I have seen it in some youtube DA runs, how it is done. There is an example at 4:28 here https://m.youtube.com/watch?v=pjjuREDI744&t=492s&pp=2AHsA5ACAcoFFGFudG9uIGRlYWRseSBhc3NhdWx0

After stopping the chain attack the stun bar is still multi color in his case. Then with heavy attack it seems to trigger the chain attack once again. I haven't been able to reproduce it, the stun bar turn gray when I stop it.

Edit: ok it only work on Boss, I was trying unsuccessful in VR but it worked in DA. I guess it is useful to skip supports chain and get the DPS chain attack twice.