Incomplete page loads on admin side

Recently (I’ve seen this with 5.9 and 6.0) certain pages do not fully load on the admin side. Widgets is one (where we get some or most of the widgets we can use but none of the widget areas on the right, nor the footer indicating that the page stopped loading). The other key area is when I try to open Customize on any front-end page. What I get is a tiny amount of content (related to selecting a gravatar) and then

Fatal error: Allowed memory size of 268435456 bytes exhausted (tried to allocate 14061568 bytes) in /var/app/current/public/wordpress/wp-includes/user.php on line 1150

We had this happen a year or more ago with an earlier version of jetpack and the issue was eventually fixed. Until we can figure out what is causing it this time (same or similar bug? Something else?) we’ll be rolling back to the latest version that does not cause this (next up: 5.8…)

If I deactivate Jetpack, everything works fine.

Thanks

-A