Server on O365 Target Release was upgraded LATER than the server on O365 Standard Release

[TanyaVynar]

Nature of issue

It looks like our test Exchange Online servers on Target release get updates much later than customers' servers on the Standart release.

How it was detected

The FindItem requests was processed by EWS in a wrong way, this was causing issues for our product. This issue was found on customer's side (EWS v15.20.4219.9 at that time) and was not reproducible on our side (our EWS had v15.20.4195.17). The issue with FindItem request was reported to MS support as Case 25953710 (#267).

Preliminary investigation

Severity and Impact
Thousands of production users (Standart release) were affected by the mentioned issue. No users on our side (Target release) were experiencing this problem.

Attempts to isolate
The issue started to manifest itself on June 2, about 8AM UTC without any changes on the application side, so update or change to Office 365 Exchange Online is a suspect.

Scope

Office 365 ONLY. Exchange 2010-2016 doesn't have this issue.

Office 365: Only part of the customers are affected, while other part of customers is working fine. Possibly because of staged updates of Office 365 instances.

The issue is definitely seen on Office 365 Exchange version: 15.20.4219.9

The issue seem to not reproduce itself on: v15.20.4195.17

Narrowing down problem

So for some reason, customers received updates before us. We would like to clarify why did that happen.
And the main question is, how to get those updates for our Test Exchange Online server to reproduce mentioned issue on our side?