Having same issue with rewind on Live TV.
Roku Ultra 4660x
Channel Version 2.5.0
Roku Software Version 8.1 Build 4090-46
WD Elements 25A2 1019 2 TB with 1.77TB Remaining
Mark from Tablo Support upgraded me yesterday to 2.2.19 because of the missing recordings issue. I can attest the rewind issue was present on both .18 and .19 firmware.
(Edited to reflect complete Roku Software Version)