People who start yoga usually notice strength changing before range of movement does. The asymmetry reflects the fact that flexibility is limited by several different things, only one of which responds quickly.
Range is limited by tolerance as well as by tissue
The end of a stretch is usually reached when sensation becomes unacceptable rather than when tissue has physically run out of length.
That endpoint is set by the nervous system, which restricts range as a protective response before mechanical limits are approached.
Much of the immediate gain from stretching comes from shifting that tolerance, which is why range can improve within a single session and be gone by the next day.
Structural change is slow and partial
Where lasting change occurs, it involves remodelling of muscle and connective tissue in response to repeated loading at length.
Those tissues adapt over months, and connective tissue is slower than muscle, which sets the pace for the whole process.
Strength, by contrast, improves early through better neural recruitment, so a beginner sees results in weeks and interprets the difference as a personal limitation.
Joint structure sets limits that do not move
Bone shape and the depth of a joint socket vary considerably between individuals, and both impose ceilings that no amount of practice alters.
Hip architecture differs enough that two people practising identically will reach visibly different positions, and neither is doing anything wrong.
Pushing past a bony limit does not produce range and is one of the more common routes to joint irritation in flexibility practice.
Range without strength is unstable
Achieving a position passively does not mean the joint can be controlled there, and control is what determines whether the range is usable.
This is why loaded work at long muscle lengths has become more common in flexibility training, since it develops range and control together.
It also explains why flexibility gained through passive stretching alone tends to disappear during periods without practice.
Daily variation is large and normal
Available range fluctuates with temperature, time of day, recent training, sleep and stress, and the variation between two consecutive sessions can be considerable.
Judging progress by a single session is therefore unreliable, and comparing a morning practice with an evening one is not comparing like with like.
Pain that is sharp, that persists after practice, or that involves numbness is not a flexibility issue and warrants assessment rather than more stretching.