How could an error during transcription affect the protein that is produced?

An error during transcription could produce a shorter protein or induce changes in the protein's sequence.

Explanation: Transcription is the process of single-stranded RNA synthesis from a DNA template (gene). During this process, RNA polymerase reads the DNA template and synthetize RNA, keeping the sequence. The RNA sequence will be reading later by ribosomes and protein will be produced. An error in transcription could produce changes in codons that are sequences of 3 nucleotides that determine  aminoacids of the protein, and that would change protein folding and inactive it. Another possible result would be that  error in transcription produce a premature stop codon that cause a shorter inactive protein.

most community's take hundreds of years to become stable

2%? i tried finding the exact sorry if it's not 100% correct ; -;