The lack of bikes has been a problem for quite some time, but especially after Duke's day the system has become nearly unusable. Apparently most stations have charged bikes but they do not appear on the app or cannot be used, much to the discontent of Vel'oh users. Some Reddit users suggest that some stations had been closed off for Duke's day and that the app might not yet have been updated, leading to the mentioned problems - but that is speculation.
There seem to be several other reasons for the lack of bikes. Recently, the number of subscribers has increased from 9,500 to 13,500, and there is a total of around 900 bikes in the system. This increase reflects the great success of the service but also leads to the consequence that fewer bikes are available, especially during rush hour.
Moreover, bikes have started to break more frequently, apparently because of people using them to transport more than one person at a time. After a bike has been broken, it needs to be taken out of the system in order to be repaired.
The unusually long period of good weather might also be a factor that contributes to the lack of bikes. People are more likely to get on a bike and cycle to work instead of getting on a bus when it's warm and not raining.
The service is certainly a good idea and, as the number of subscribers show, people like it — but if it continues to disappoint its users they might end up turning away from it.
Reddit thread and photo source: What is up with the Vel'oh service lately?
