Why is a successful clone incorrectly digested?

1. Do you have the sequence of your vector? It is possible that there are other sites in your vector that you use restriction enzymes, causing the enzyme to cut the gene away from the vector and cut the vector open, so that you get multiple bands of different sizes. Or there is a cleavage site in your gene of interest, causing the gene to be cut into several segments.  

2．If the size of the band you get is not much different from the size of your target band, then there may be a marker error, the possibility of this error is relatively small, but I have indeed met before, if you have repeated several times and they are all this result, you can try to send one of the clones to sequence, according to the sequencing results to analyze the reason. When sequencing, it is best to measure both ends of the gene separately, and it is recommended that the sequencing primers be designed so that the results can show the situation at both digestion sites.