Games : My industry is suddenly abanding buildings due to a lack of workers

Rather suddenly my industry district started to look like this, with a lot of buildings abandoned:

If I check the buildings, the stated reason for abandoning is a lack of workers. I looked at the city statistics, but I can't see any reason for the sudden lack of workers:

The number of jobs is stable, the population increased. This doesn't make any sense to me. Any idea what causes this and how to fix the situations?