@saludcontigo, I made a quick check with the xlsform you shared. I slightly modified your xlsform to check. The modified xlsform is as follows:
survey tab of the xlsform:
choices tab of the xlsform:
Reference xlsform:
aUy4NispBxbpn5mAfKt9wp.xlsx (11.1 KB)
So when checking with the xlsform (shared above) I observed that the data when collected with Enketo I was able to submit the data to the server similarly while collecting data through Collect android app I got this error message:
So I again edited the xlsform and then removed the 
, 
and 
button from the expression used under the calculation column and then I could submit the same through the Collect android app too. So, here my preliminary guess is that the calculation column is not supporting the icons you are trying to use.
Maybe @Xiphware should be able to add more to my observations.
