Yes. Symptoms can happen during rounds and/or between rounds. Some of my worst symptoms happen after I've stopped the round. Some of this may also be some redistribution symptoms that are unavoidable when you stop the round.

There could be more reasons. You maybe on too high a dose at this stage and need to reduce it. Or you may need to reduce more blood/body levels of mercury with DMSA alone for longer before trying ALA again. It may also be the fact that ALA does not suppress symptoms like DMSA does, so often people can find it harder. Using DMSA with ALA can make it easier.

Hard to say. I'd do what you have contemplated. Wait till things die down and try the DMSA alone and see what happens. Just reducing the dose can be helpful too. Sometimes it can also be that some people may need to take it even more often. Every 3 hours, or in some cases, even every 2 hours. I think this is due to those that metabolise it faster and need to take them even more often. So sometimes one has to adjust dose and/or timing too.