If I understand you correctly you did not have a supervisor or a faculty member you worked with closely before you left. In that case I think your best chance is to contact the department, explain your situation and ask them if you could either join the program again off cycle or if they would consider your application, if you applied again next cycle. If they accept you again immediately that’s great. However, most likely they wont but they will allow you to apply again. In that case I think that you can immediately get in touch with faculty members (ideally people, you have talked to before) and discuss potential dissertation topics. That way you would not lose too much time and you have strong support in the faculty once the next application cycle starts. You may want to stay in your current PhD program until the next cycle for funding reasons and do the minimum work required for that. Alternatively, there may be someone who would hire you as RA at your old department.

During the next cycle I would do a full round of applications to all interesting schools because there is no guarantee you will be allowed back into the same program. However, even if you have to settle for a lower ranked school, you will still have connections in your old department and may be able to go there for a visit during your PhD or Co-Author with people (if field X does not require Co-Authors to be in the same place because they need to share a lab or other physical resources).

If I understand you correctly you did not have a supervisor or a faculty member you worked with closely before you left. In that case I think your best chance is to contact the department, explain your situation and ask them if you could either join the program again off cycle or if they would consider your application, if you applied again next cycle. If they accept you again immediately that’s great. However, most likely they won't but they will allow you to apply again. In that case I think that you can immediately get in touch with faculty members (ideally people, you have talked to before) and discuss potential dissertation topics. That way you would not lose too much time and you have strong support in the faculty once the next application cycle starts. You may want to stay in your current PhD program until the next cycle for funding reasons and do the minimum work required for that. Alternatively, there may be someone who would hire you as RA at your old department.

During the next cycle I would do a full round of applications to all interesting schools because there is no guarantee you will be allowed back into the same program. However, even if you have to settle for a lower ranked school, you will still have connections in your old department and may be able to go there for a visit during your PhD or Co-Author with people (if field X does not require Co-Authors to be in the same place because they need to share a lab or other physical resources).