Today, we were doing SM Calphayus on pubs. The boss reset on us twice going into the third past/future phase. Within about 10 seconds of entering it, the boss reset and we had to kill him all over again. We are pretty sure it is because the main tank is going into the past while the off tank is going into the future. As a result, the boss can't find the main tank (who has aggro) since he is not in the future and resets. If we could fix this problem (aggro dump?), I know my raid would really appreciate it.

Thank you for your time.

Yes, we've seen this happen as well. The boss would stand still so that the tank cannot move him, and a few seconds later he will reset.

However, it is easy to prevent this from happening. It does not matter if only one or both of your tanks are in the future. Just make sure that the tank who first taunts the boss gets in melee range before taunting. When he taunts directly after entering the portal, he is too far away from the boss. Either do a Force Leap or walk towards him, then taunt.

Regarding the strategy for the final phase:

If it helps, we always have one of our healers get the first holocron. That way, both tanks can get into the future. Then, one tank will taunt the boss for a few seconds and use all his defensive cooldowns. The healer calls out when he is halfway through with the holocron so that we can do a tank swap. The tank who first had the boss will go get the second holocron, while the other tank (who still has all his defensive cooldowns available) will now have the boss. When the healer has placed the holocron, he can also go into the future and help doing damage since the tank should not require healing while he has the holocron.