Apple has told Authorized Service Providers to expect customers who are unable to connect to a Personal Hotspot or experience frequent disconnection from one. Customers may also experience general issues with data performance.
Some users have been reporting problems with Personal Hotspot as far back as iOS 13.1.2.
As a temporary workaround, service providers have been instructed to toggle Personal Hotspot off, and then back on. This suggests that there is likely to be a fix in a future software update, but it is unclear if the issue has been resolved in iOS 13.4, and the latest GM release notes do not mention any Personal Hotspot fixes.
Apple recommends that customers keep their software up to date and said that this is not a hardware issue.