Sync issues with filter

[matfax]

Filter seems to write the set's underlying map at some point and this leads to multithreading issues.
concurrent map read and map write

[issue-label-bot]

Issue-Label Bot is automatically applying the label bug to this issue, with a confidence of 0.94. Please mark this comment with 👍 or 👎 to give our bot feedback!

Links: app homepage, dashboard and code for this bot.