Looping samples only works outside the Waveform view

[slujr (•X∑NøB∆B∆•••)]

These instruments and tools might also help •GRAIN SCRUBBER• xrni which allows you to offset sample start position via macros, so you won’t have to wait for the whole sample to play to hear the loop.
New Tool (3.0): Loop Control
And
New tool (3.3.2): Sample Multi Controller v2.1 build 060 - Get more out of Renoise’s sampler! both of these tools offer more flexible loop control