What is the problem?
Portfolio for JIRA commit to JIRA issues scheduled releases and members only in case they were set (or fixed) manually.
In case below August Release will not be commited to SAP-54, because it was scheduled by Portfolio and not fixed manually. We see Calculate Option.

And now August Release will be commited to SAP-54, we see that there is August Release option, not Calculate.

That what we call "fixed" Release. The same with members.
In case below Mark is scheduled by Portfolio to SAP-54, but he will not be assigned to SAP-54 in JIRA, because he is not fixed in plan, we see - No constraints.

To commit Mark to JIRA issue, we need first manually to fixate him:

Also we may need to "fixate" Release or Members for some issues in case we want they weren't changed with the next Calculation.
Curenttly with Portfolio you may "fixate" Release or Members for each issue separately, one by one. It may be quite annoing.
That's why we created possibility to fixate Releases or Members in bulk.
How to fixate/unfix Releases or Members in bulk?
- Check issues in Scope where you want to fixate or unfix Releases or Members
- Add Releases column to Scope in case you want to fixate/unfix Releases
- Add Members column to Scope in case you want to fixate/unfix Members
- Press Fixate Releases/Members in case you want to fixate them
- Press Unfix Releases/Members in case you want ti unfix them (these buttons will appear after checking at least one issue ib Scope)

https://jira.atlassian.com/browse/JPOSERVER-1390