hi, there seems to be a limit.
I checked the Ubidots lib and they say this:
Important: The max payload lenght is 700 bytes, if your payload is greater it won’t be properly sent.
You can see on your serial console the payload to send if you call the setDebug(bool debug) method and pass a true value to it.
source is here.
EDIT: so it is not only a matter of number of variables (in your case 10) but the size/content of them. Meaning in some cases you would be able to successfuly send 10 variables, but under some conditions you would be able to send LESS (or even more!). That’ll be hell to troubleshoot. BEware.