Setup
In the Active sprint board we have Quick filters set up to filter tickets for a specific platform. We have a filter for 'iOS' and a filter for 'Android'. The query for a filter is simply 'summary ~ iOS'.
Then, in the sprint we have story tickets, with each story having 2 subtasks, titled 'iOS' and 'Android'.

Issue
We've been using the quick filters for years now, but since a couple of days the filters aren't working for us anymore. The filter only seems to show 'main' tickets, that fit the conditions, and does not display the subtasks.
So a ticket called 'Fix .....' with subtask 'iOS' does not show up in the 'summary ~ iOS' filter, but a ticket called 'Fix iOS .....' with subtask 'iOS' does show up in the filter.
A couple of days ago both cases would show up when using the iOS filter.
Any idea's what we can do?