Good translations of the Gospel of Mark tell us that the end of Mark's Gospel is disputed. The NRSV gives the three main options. There is either the traditional ending which included Mk 16:9-20; a shorter ending which includes one verse which summarises the spread of the gospel through the disciples; and some end at 16:8. Most scholars are of the view that 16:8 is the end of Mark's Gospel.
This ending raises all sorts of questions. Why does Mark end so abruptly with the women disobeying Jesus and hiding away in fear and perplexity? Why does he include no appearances when the angel has told the women to tell the apostles to go to Galilee where he will appear to them? Why does it not include the appearance to Peter (cf. Jn 21; 1 Cor 15:5) or to the twelve; considering that Papias tells us that Mark is dependent on Peter's testimony (c. AD130)?
This is a great question. Some believe that Mark ended it that way to highlight the perplexity at Jesus' identity, one of the recurring themes of the Gospel. Some think the ending has been lost. Some accept the authenticity of one or other of the endings.
It is a fascinating question for sure.
My own view is that it ends at 16:8. However, I am of the view too that 16:9-20 is still a valuable resource. Most copies of Mark include it and it correlates with the testimony of Luke and John. It is early, if not as early as Mark (perhaps late first century/early second century). It reinforces the commitment of the early church to evangelism, signs and wonders; its belief in the ascension, the exaltation of Christ and the Great Commission.
Anyway, I have no solution to the problem myself; but it is a good question.