So. Rek'Sai's on the PBE but the Boards are currently experiencing technical difficulties, so it may be tough for you to post - or for us to respond. That said, this is a temporary post to let you know that the Rek'Sai team is reading and reacting to your feedback / bug reports, even if we don't reply to a specific thread.
There *are* some known issues to watch out for while burrowing on the Rift while we continue to get her ready for release.
* Burrowed Q (Prey Seeker) does not grant vision of targets hit.
* While burrowing around large walls, Rek'Sai's position can sometimes become de-synced from her tunnels.
* Using a tunnel while in Void Rush can cause Rek'Sai to be unable to cast other spells. Currently the only way to fix this is to die and respawn.
Please let us know if you spot anything else, and let us know what you think. When the boards become defunked, we'll split this post up into a general feedback thread and a known bugs thread, but we'll still be keeping an eye here!