As others have said, the reason the timing is off is because your DPS has increased as you gained more gear and general confidence with the fight. Please note that renaud pop times are NOT connected to phase changes. They simply happen at timed intervals from the start of the fight, independent of when phase switches are triggered. As in, when the first phase change happens, there is a possibility that the renaud will pop at an inopportune time if you aren't careful. My group has found that the easiest way for the kiter to handle renauds is if the renaud pops at about the same time the FIRST phase change happens (80%)... so basically, your kiter is placing the 2nd renaud when the first of three adds pop. To make this possible, ensure that THREE voices happen BEFORE the phase change. By the time the 4x adds spawn (60%), your 4x stack of renauds SHOULD be in place unless you get unlucky with where renauds spawn and they need to be killed because they aren't stacked properly. However, you will still want to wait for a voice to happen before the phase shift because otherwise the renauds might unfreeze.

The most important thing, as others have said, is the final phase. Wait until your group experiences a voice to shriek combo before pushing the boss to 35%, as it is essential they get refrozen due to the timing of the next phase. The final add will also need to die ASAP. If it doesn't, your renauds might run out of time. So, my group uses LB on the final add. We used to get LB3 but now we are only getting LB2, so have your dps be mindful of that. If you DO run out of time on the renauds, kill them off rather than 'risking it' because if you do risk it, your entire group might end up wiping. It is possible for your kiter to handle placing new renauds in this phase, as stressful as it is... I've done it several times, even while dodging shrieks and ensuring shrieks were 'hidden' from the group because they were on myself.

Ideally, though, watch phase pushes so that you won't have to deal with placing renauds at all after the first four are properly positioned. Have healers (or whoever you have assigned to voice the renauds) as well as people with shriek ensure that ALL FOUR RENAUDS are hit so that the kiter knows their job is 'done'. Only the kiter should kill misplaced renauds, and if you do accidentally kill one let the kiter know so he or she knows that a new one will be spawning.