Teeth Not Aligning, Dentist Suggests To Go To Previous Trays, Is This Normal? (photo)

I could definitely see this as a problem if you have not been wearing your aligners 22 hours per day. However, if this is not the issue, I would be concerned that you are having these "tracking" (the space you are seeing at the tooth/aligner interface) issues at the 5th aligner. I would consult with your provider and have him/her review the treatment plan with you along with the Clincheck video that shows every stage of your treatment. Each stage in the video should correspond to the corresponding position of your teeth. If it does not, it is probably a treatment planning issue caused by improper use of attachments, trying to achieve excessively difficult movements or improper planning of IPR (space requirements to achieve tooth movements).  

It is possible that at times the teeth 'fall behind' or do not move along with the Aligners. 

Make sure you are wearing them according to the instructions given by your Orthodontist (or the general dentist, if that is who is doing it for you).  Ideally, you should be wearing them about 21 hours/day.  If it is less, one of the things we see, is that teeth start to be left behind.  This should be addressed earlier rather than later, as with each subsequent aligner, the tooth tends to fall further behind. 

Therefore, it is not uncommon to at times go back a few aligners to pick up the tooth that is falling behind.  

Depending on your compliance with the amount of hours that you wear each tray it is possible for some of the teeth to fall behind. Sometimes it helps to go back to the tray that fits properly and wear it consistently to get the teeth back on truck.