Error when loading web collect: Unexpected token < in JSON at position 0

I successfully uploaded and deployed an XLS form via XLSForm Online v1.x. When trying to enter data via the web collect link, however, we’re receiving the following error intermittently (like very 2 or 3 times we try to load the form):

Error occurred during the loading of this form. It is recommended not to use this form for data entry until this is resolved.

Unexpected token < in JSON at position 0
Any suggestions on what in the coding might have caused this error and how to resolve it?

Could you attach that form?

SUFAL_BEAT_INFO_2021_Final.xlsx (451.7 KB)

Hi good morning! I already shared with you xls form.

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this is happening when I am trying to convert xls to xml from following link

Hmm I don't know what's wrong maybe the form is too big? @martijnr do you know what's going on?

Dear I solve this issue but I don't know how. I just minimize some group. and remove default value from some field.

I believe the issue is/was that something times out and Enketo's internal response is whatever error occurs which in this case is HTML generated by nginx (?), whereas Enketo normally responds with JSON to that call. So it's sloppy error handling for sure, but the underlying issue is something timing out.

When I am going to edit in tab second time its show attached error. Is it android apps problem.