Why there are missing pixels in Sentinel 3 SYN products?

I downloaded and visualized SYN product(S3A_SL_2_SYN____20210207T042350_20210207T042650_20210208T133428_0179_068_147_2520_LN2_O_NT_004).
In reflectance product:
I noticed that there are missing pixels over water bodies, over clouds, on snowcapped mountains and also on openland of Indo gangetic plane.

Can anyone provide reason for this.


as said in this User Guide the SYN product provide surface reflectances over land. That’s why no data is provided over water and when there are clouds no surface reflectance can be computed. I don’t know why there is no data for some snow areas, for sure. Probably the reflectance retrieval failed for some reason.
When locking at the data all seem to be properly flagged. For example, the snow areas in the mountains are flagged with SYN_flags.SYN_cloud.
For more information on the data I suggest reading the documents provided by ESA.
For example the product guide SYN Level-2 Product - Sentinel (esa.int) and in the product library you will find more details:
Sentinel-3 Synergy Document Library - Sentinel Online - Sentinel (esa.int)
Check also the SYN Algorithm Theoretical Basis Document

Thank you for the hints @marpet
Additionally, in the same product(S3A_SL_2_SYN____20210207T042350_20210207T042650_20210208T133428_0179_068_147_2520_LN2_O_NT_004), the alluvial plains of Indo-gangetic plain, were flagged as Cloud and partly_cloudy. That indicates a false negative flag.

If you have issues with the data, please address you question to the data provide.
In your case the best contact point is: EOSupport@Copernicus.esa.int

A screenshot would also help to explain your issue. Why do you think the flag is wrong? How do you know that there were no clouds? Do you have other data at the same time?
This information would help the Copernicus support team.

I arrived at the conclusion of False negative cloud flag in the above mentioned SYN product, since the respective date’s SL_1_RBT product shows almost clear sky conditions over the Indo gangetic plain.
I shall attach the screen shots soon.