I noticed yesterday an unknown label, 'ˆf_bisa' appearing in Gmail. I assumed it had been created by my son messing with the keyboard whilst he was watching YouTube earlier (not yet 5 and already a Lego Ninjago fan), and deleted it.
I thought nothing more about it... until I noticed it was back today. I have tried deleting it a few times, but it refuses to go. I'm assuming it is a bug, possibly due to the synchronization between Gmail and the iOS Mail app? Regardless, a search shows I'm not the only person experiencing this issue:
Both posts have appeared on Gmail forums in the past few days complaining about the label. Nice to know I'm not alone. Apologies to anyone who has come here looking for an answer - I haven't a clue what is causing this. If you know, please get in touch!
Update - 13/08/2021
I came across this article that suggests it may be due to a third party read receipt script hosted at https://t.sidekickopen45.com. The subdomain t.sidekickopen45.com redirects to the page https://www.hubspot.com/abuse-complaints. Sidekick also used to be the name of Hubspot's email tracking tool.
Further Update - 20/08/2021
In the original update, I mis-identified the company that was behind the read receipt script. Apologies to those concerned. Thanks to Derek/Dmitry for reaching out to let me know.