WordPress stalls intermittently with latest IThemes Security

Upgraded to WordPress 4.7 recently and everything seemed fine at first. After a day or two I became aware that page loads would stall intermittently, rendering a blank page. However you’d frequently get lucky and the page would load.

My first instinct was that it had something to do with IThemes; I know from experience that it can cause weird access problems. After deactivating IThemes, sure enough, the problem went away. I’ve been rechecking all day and the problem has not returned. Upgraded to the latest IThemes (6.0) in the hope that the problem had already been observed and fixed, but it didn’t help.

Has anyone else seen this? Or does anyone have a possible work around? It’s possible that the problem is in one particular feature (which I could turn off); but which one? Reverting to a previous WordPress version might help; but am reluctant to do that since everything else is working fine.

TIA for your help.