Wandb line plots only show bar charts after refresh

Question

My weights and biases (wandb) panels (e.g. for loss) shortly show line plots (x: steps, y: loss), then refresh (showing a spinner for some time) and then only show bar charts.

Editing such panels either shows (a) "Select runs that logged eval/loss to visualize data in this line chart." on the left or (b) "Showing a bar chart instead of a line chart because all logged values are length one." on the right.

Does that mean that (a) a value eval/loss is not found for the runs, or (b) only one value is given per run? How can I change this? But why was there a real line plot shown for about a second, before the panel refreshes? Where there values dropped? Why?

Panels shortly show line plots:

Then panels refresh and only show bar charts:

Code

I am using huggingface transformers TrainingArguments with argument report_to="wandb" (but with the default logging_steps of 500). I am doing 10-fold cross validation without any explicit wandb.log call within the cross validation loop. I do all of this in the train() function, which has as last command wandb.finish(). train() is called via wandb.agent(sweep_id, train) as I am using all of this within a large sweep.