Basic accessibility features for colour blind users lagged behind GitHub for years, making it difficult for me to even review diffs and work out what had been removed/added. In the end, I think the customisation feature only got shipped because an external company opened a merge request - and parts of it still fail WCAG AA today.
There's no longer a gap when it comes to GitHub and GitLab in terms of CI support, and I really don't think some of the e.g. Kubernetes integration functionality justifies picking it as the canonical location for an organisation's code.
Recently they've had to start to cut back on storage limits (and had to 180 on deleting repositories to try and free up space), which casts doubt in my mind on their financial stability.
Really though, I'm just fed up of having to put up with using it day-to-day, because clients I work with decided it would be great to pick it X years ago when GitHub wasn't as feature-rich. I now look at companies who cheap out and run self-hosted GitLab/GitLab.com with some suspicion, and question why they're not using the de facto standard tool for the job. I look at it the same as if I found a Java shop that didn't use JetBrains' products for development, it's a red flag.