Beta UK have identified a problem with some 2014 Beta Evo 2T bikes where the rivet in the gear selector has dropped out. This has only happened in about 2-3% of bikes, however they I feel it would be correct for riders to check the selector in all bikes. You should find the selector rivet in place. You should centre pop the rivet which you can do on a hard surface which will ensure the rivet cannot come out. The diagram shows a faulty selector where the rivet has dropped out. You can see the rivet has been riveted using a machine but it has not been done correctly. The rivet should be located in the hole.
To do the job you must take out the rear sump bolt then find a wedge to hold the sump down 2-3cm. You must then remove the clutch. The selector will then come straight out. Be careful with shims on the selector shaft. You must re tighten the clutch centre nut to 70Nm using lock tight.
As so few bikes have been found with this fault it is possibly not necessary but for riders that are competing in the SSDT, nationals and British Championship etc it is a worthwhile job to do.