By default, Mastodon prevents you seeing a boosted post again until 40 other posts have flowed through your timeline. There is more info at:

➡️ fedi.tips/how-do-i-stop-seeing

The 40 number is hardcoded into the Mastodon server software and currently cannot be altered. It seems to have worked better in the days when Mastodon was much quieter.

If you're comfortable using Github, you can vote for this number to be adjustable at github.com/mastodon/mastodon/i

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If you have a fediverse account, you can quote this note from your own instance. Search https://social.growyourown.services/users/FediTips/statuses/115612532148780345 on your instance and quote it. (Note that quoting is not supported in Mastodon.)