Tropit, you sent me to Google once again
I read this: There could be a few possible reasons for a chiffon to collapse:

1. The egg white hasn't been whipped enough. ...
2. It's possible that you over blended the egg white and egg yolk mixture. ...
3. It's very likely that the oven temperature isn't high enough.

https://www.allrecipes.com/recipe/7892/chiffon-cake/
the first review seemed helpful also.
Since we have started gathering about 2 dozen eggs per day, I will give this recipe a try.
Thank you for your insights.