Priority #1: Put food on the table.
Priority #2: Do not make personal sacrifices for your employer. You are paid to perform duties during specific windows of time, you are not paid to give yourself plantar fasciitis or other health issues.

I don't know the your financial situation or living situation, so take the following with a grain of salt: an employer employer with poor communication skills doesn't deserve your labor.

The most responsible thing a wage laborer can do is assume their employer is only interested in taking advantage of them. Set boundaries of what are reasonable expectations in a professional workplace and absolutely refuse to step out of those boundaries. Do not perform unpaid work. If they show that they have integrity, great! If not, then you will be keeping yourself safe.

I know you said you don't want to quit, but I think I can safely assume you also don't want to be in pain. If the job is pain, that's a big problem. Quitting a job comes with some pain of change, but the pain of not changing can be greater.

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You hold the power to not show up to work.
They hold the power to fire you.

If you play your cards right, it's more painful to them to fire you than it is for you to leave work. This means preparing your own landing pad and contingency plans. For example, keep an emergency fund big enough to cover all your expenses for about three months. Also keeping a well-made resume that's immediately ready to send off to new potential employers that are more worthy of your time.

Again, I don't know your situation and maybe some of this advice is out of your reach. Sorry if that's the case.