we can only recommend and advise and it is down to the manager whether they act on the advice, but the rule of thumb is to act on it, as if in the future you decided to take it further it doesn't go in the employers favour if they ignored the advice.
On the bare bones of what you have written, my advice would be that the issues need to be resolved (and we mean addressed this is not a direction by OH that every greivence you have should be resloved in your favour, we do not know all the facts it is your perceptions we hear and we except that, we are not the police) so a meeting with your line manager looks like they are engaging in this, so this is good.
Now the rub, I would also advise you work days on returning as health wise especially with stress it is better way to aid the recovery, so if it was me you would probably walk away unhappy, this is because the problem is a management issue, not health (even though it is effecting your health iyswim) but on the up side if it was me I would only advise 4 -6 weeks on days and starting on reduced hours given the long lengh of time you had been off, guessing you work e/l/n it would not beyond the wit of the manager to have you on the duty opposite of the old manager so you would only have hand over time and maybe the odd shift together, as if you have made requests and so have they, the new manger can not be expected to work miricles also the skill mix needs to be kept.
The reduced hour is also down to the Line manager wants to play it, either they will just let you have the time off, but they may (especially at this time of year and the amount of leave you will have accured) take it from your leave if you have any left.
good luck.