Disclaimer: Not a health care professional.
Honestly, it just doesn't sound like the muscles are strong enough to do the move. You weren't training for a couple of months, so the injury healed. But how much strengthening happened in that span of time? Maybe not that much, since you mentioned you have (just?) started getting back to flexibility and strength training. I don't know that you can necessarily go back to the move that injured you in the first place without having done more strengthening and conditioning to prepare for that move. No pain = no more injury, but it doesn't really meant that you are ready for that same move. In fact you may have also lost some strength if you have not done anything at all in the past two months.
I'm glad you're going to a physio, they should be able to tell you how to strengthen the muscles without causing further injury. The back muscles are often overlooked when it comes to strength training exercises (especially it's not a vanity muscle - not like biceps or abs!) so you'll need to think about strengthening the back specifically. Then also think about how much weight/resistance are you using when you do strength training? Especially for people who don't weight train a lot, 12-15 lb dumbbell rows might seem like a heavy weight. But compare that to body weight - the muscles are asked to carry a lot more load in an invert than it's used to, even with that "heavy" weight training session.
You seem to be very stressed out and anxious about not being able to pole at all, ever, as the prospect of having to stop something you really love (and have started becoming quite good at, I imagine) can be really anxiety-inducing. However, a strong and healthy body should be the #1 priority, so I'd stop thinking about this problem as "What if I can never invert?" to "How can I adequately prep my body for strong, secure, and injury-free poling?" Take it slow, focus on strength and conditioning, so you can progress w/o more trips to the physio. This is more than just pole - if you can't breathe or cough or sneeze without being in a lot of pain, your health and well-being is at stake, and your body is telling you to slow down.
Finally, I'm wondering if your instructor is not well-versed on body mechanics, especially correct muscle engagement etc. when performing a move. If you have the option for a private lesson w/ someone with a good reputation for that, they may be able to correct any mistakes in your invert that's causing the muscle strains and injuries. The video Veena linked 2 months ago has a really good bit at the end on the common mistakes for inverts: one of them is jerking down (not able to hold the weight at the top of the invert) which strains the back and bangs up your ribs. That could be what's happening to you, but you can't spot it while you're doing the move yourself!
Take care of your body, rest up, and get back into it slowly!
