I've experienced this since 2018 across all versions of linux mint since 2018.
The problem appeared to be a lot of unnecessary disk io coupled with DNA lookup that only get done after every single read request is complete. This means that when tab #10 is taking long to read whatever from disk it blocks every other tab.
I'm noticing it on a fast SSD, though it's more like 5-10s after launching. No issues once it's running. I'd guess it's related to my very old and large profile.
The problem appeared to be a lot of unnecessary disk io coupled with DNA lookup that only get done after every single read request is complete. This means that when tab #10 is taking long to read whatever from disk it blocks every other tab.
Noticeable only when using spinning rust disks.