SNAP 6.0 can't read bands by rayleigh correction in graph builder

Rayleigh correction works well for single image. But when I try to build a graph, it’s blank in source bands.

The Graph Builder can’t handle the processor properly.
If you only want to perform the rayleigh correction then select the Rayleigh Correction from Optical / Preprocessing in the menu. If you want to process multiple products in batch mode then you should create a graph xml file and use it on the command line with gpt.

I have the same problem, but only with the new vesrion 6.
The previous version worked fine with batch processing multiple images for rayleigh correction (through graph).
Do you think I should go back to the previous version or there is a chance of fixing this issue??

I wonder how it could work in a previous version.
I would suggest using the command line for processing. This page might help you:
Bulk Processing with GPT
I can’t say when it will be fixed.

I have no idea, but I reinstalled ver. 5 ( keeping also ver. 6) and still works perfectly!!

You are using the rayleigh correction for Sentinel-3 data, right?
Then it works in the earlier version. But with version 6 also Sentinel-2 support was added and also the possibility to select the bands.
And this band selection prevents the usage within the Graph Builder.
The Graph Builder needs to be enhanced in order to be able to deal with it.
As suggested you can use the command line or use the standalone processor from the menu Optical / Preprocessing / Rayleigh Correction.

You can try to save the incomplete graph to disk and then update the XML file in a texteditor. You can generate the parameters you need with the standalone processor. After configuring it, select in the processor dialogue select File / Display Parameters…. The shown snippet can be pasted into the graph.
Once you have the graph, I think, you can use it in the Batch Processing window in SNAP.