I've recently bought two different lots of bluepills that don't work with this bootloader but they work fine with the STM32duino-bootloader, and user space USB works too.
The chips are marked as STM32F103C8T6 but I'm sure they're fake just like most of the bluepills I've bought over the years. At first I thought I'd just received a bad batch, but it looks like many vendors are selling this new clone variant because I then got the same type from another seller :(

They symptoms seem to be they're just running too.... fast? On a 'good' bluepill PC13 LED flashes at ~20hz after burning the bootloader, but on these new ones it flashes at 60hz.
The good bluepill receives its first SOF ~150ms after the start of enumeration, whereas the new bad one receives it 1ms after starting to wake the host.
But with the STM32duino-bootloader flashed on the new bluepill instead, it too takes ~150ms too.

With STM32_HID_Bootloader both bluepills receive the SETUP and DATA0 packets from the host about 40-50ms after the first SOF, but these new bluepills never send an ACK (or any response to the SETUP).
The host retries the SETUP transaction two more times without an answer, then tries 3 more times 400ms later.

Seeing as these bluepills work fine with other USB bootloaders the hardware is obviously capable of establishing a USB connection, which leads me to think there might be something in the initialization that they don't like?
Any help would be appreciated, I've got a dozen of these now and I assume there's lot of other people receiving them too.