sklearn package with AttributeError: 'MissingValues' object has no attribute 'to_list'
The problem was with the pandas version. I've used Python3.6 as interpreter and pycharm would only let me install version 0.25 pandas. Now I am on Python3.8 and pandas 1.2.3 and the minimum code example provided by @Oxbowerce works now. I'll be more careful with checking the dependencies in future.
The sketch goes into the epochs now, there was just a minor labelling error:
Traceback (most recent call last):
  File &quot;C:/Users/bobin/PycharmProjects/Mussel/cnn_musseltest.py&quot;, line 348, in &lt;module&gt;
    plt.plot(history.history['acc'], &quot;g--&quot;, label=&quot;Accuracy of training data&quot;)
KeyError: 'acc'

Renaming 'acc' to 'accuracy' and val_acc to val_accuracy helped, as stated in the warning log.
WARNING:tensorflow:Early stopping conditioned on metric `acc` which is not available. Available metrics are: loss,accuracy,val_loss,val_accuracy