Yes, we've started seeing similar behavior in some tenants as well.
There appear to be two separate changes:
Personal Developer environment naming – New environments are now often created with just the user's name instead of the previous naming convention (for example, including "Developer" or a suffix). This makes it difficult to distinguish when a user has multiple Personal Developer environments. At the moment, I haven't found a tenant setting to change this behavior, so it may be a recent platform change.
Environments disappearing from the list – We've also observed cases where Personal Developer environments no longer appear in the standard PPAC environment list after a period of inactivity, even though they still exist. They can still be found using Advanced Search, and adding yourself back as an Environment Admin makes them visible again. This seems more like a portal visibility issue than the environments actually being deleted.
If multiple organizations are seeing the same behavior, it's worth opening a Microsoft support ticket so the product team can confirm whether this is an intentional change or a recent regression.
Out of curiosity:
Are these Managed or unmanaged Personal Developer environments?
Is this happening in PPAC only, or do they also disappear from the Maker portal?
Have you noticed whether it correlates with the recent inactive Personal Developer environment cleanup policies?