There have been many reports of loss of Apple Pencil Pro haptics subsequent to the iPadOS 26.5.2 update - and as such it is reasonable to conclude that the update introduced a bug that will need to be resolved, by Apple, in a future OS update. Reports also indicate that a full factory restore will not clear the problem.
You and others that encounter this issue need to submit a Bug Report to Apple via its Product Feedback portal:
Feedback - Apple
When submitting your Bug Report, please ensure that you include details of your iPad model and installed version of iPadOS within the body-text of your report along with details of the problem. Do not rely upon the pick-list alone - as this rarely includes the current version of iPadOS.
Every Bug Report counts. Unless reports are submitted (with adequate detail), Apple may not assign resources to investigate and correct the issue.
In addition [i.e., not as a substitute] to submitting a Bug Report, you might also consider seeking assistance directly from Apple Support. You can contact the Support Team using the Support link at top-right or bottom-left of this page; you can initiate and manage your support cases from Apple devices using the excellent Apple Support App. If not already installed, the App can be downloaded from the App Store:
https://apps.apple.com/app/apple-support/id1130498044
