A new record type for Opportunity was created then a new Lightning Record Page Layout for it. The user record (Sys Admin) that did this work sees the old page layout even though the correct record type is chosen. The lightning record page layout is assigned correctly.
I log in (also Sys Admin) and the correct Page Layout shows. I re-checked Page Layout Assignment, user records, changed to the same role and ensured the same profile of Sys Admin on both user records.
On my computer I used the "Login As" feature of the first User and the page layout shows correctly. N.b. For all but the original user the correct page layout shows for viewing a record and creating a new record.
First user clears cache, tries a different browser, tries a different computer, tries incognito mode all to no avail. The first user just can't see the new page layout.
I clone the Lighting Record Page Layout, delete the old one and re-do the Activation. Doesn't work still for the first user.
I setup a classic lightning page for that record type. Assign it. Unassign it and re-assign it. Still doesn't work for the first user.
I change the default record type for Opportunity to be the new record type created. I ensure from the Sys Admin profile that that record type uses that page layout.
I create a brand NEW user record for the first user with Sys Admin profile, he logs in on that user record (including multiple browsers) and still sees the old page layout.
When testing from my account and when testing logged in as the first user (both of his accounts) it has never failed for me but by sitting next to the user I can clearly see it is not working for him. User error isn't the issue here.
I login as the first user (from his USER record we don't share passwords) and change an existing Opportunity to the new record type and immediately get the correct page layout.
It sounds like a caching error but we long ago turned off persistent caching in this sandbox and I've since verified this. Also it wouldn't explain why multiple browsers and a different computer don't solve the problem for the first user.
I'm desperate, can anyone suggest something?