You are right @congthien! Well, I went through several checks and cannot seem to get my child theme (with many customizations) back working:
1. tried to update another theme (for multisite) & got a big nasty error. I promise I’m not exaggerating; I was in IT for 18 years & really didn’t like it when users were overly dramatic.
2. changed theme for https://www.xbydesign.biz. Site appeared as expected for that theme.
3. tried to update the same theme as in step 1. it updated fine.
4. changed theme back to my OnePress child theme. White screen again.
5. changed theme to OnePress Parent theme. Site appeared as expected without my customizations
6. changed back to my OnePress child theme. White screen again.
Each time I made a change, I cleared my cache & checked the site in an incognito window. So I suppose now I am back to square 1 & will have to recreate my child theme. But this only happened after the update & my analytical mind needs to figure out why. In the meantime, I’ll have to take my site down again & start over.