Why can some transcript versions not be added to the AlamutTM Visual Plus database?

Several RefSeq transcript versions cannot be added to the Alamut^TM Visual Plus database, due to significant mismatches with the reference genomes GRCh37 and GRCh38. Alamut^TM Visual Plus uses Splign (https://www.ncbi.nlm.nih.gov/sutils/splign/splign.cgi), a RefSeq alignment algorithm, to ensure that transcripts align successfully with the reference genomes before adding them into the Alamut^TM Visual Plus reference database.