To bring you up to speed, this is an issue with both second generation iPad Pro, the 10.5 and the 12.9.
Many have reported it, both here and on the Audiobus forum, and to Apple Feedback, but some have claimed not to be affected.
In the last couple of days a possible explanation for this has emerged. Audio apps appear to have the latency issue IF they have been given microphone access (the microphone is ON). If microphone access has been denied (the microphone is OFF) then early reports indicate that the latency does not develop. This needs further testing.
There has been speculation that this might be the same as the widely reported crackling bug with the iPhone 8 but rumours are that this has been fixed in 11.1 on the iPhone 8 but WillOz says that it is not fixed on the iPad Pro II.
[Apple obviously listens to the complaints of iPhone 8 users but it appears that the musician community may be (relatively) too small to worry them at the moment.]