Are you getting User and event data retention message when trying to open analytics with two buttons, ‘Save’ and ‘remind me later’? Check out the solution here that I summarized after reading the article.
How User and event data retention works
In simple words your data will be deleted after selected period. Data retention meaning is to keep the data for certain time period.
If you want to keep the data more than default value you can change the value from drop down. This will give direction to Google about deleting and not deleting your data.
Check data retention options available and select wisely because end of day it is your data.
Do not automatically expire
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