Currently it is not possible to export account data using the mobile apps, if you switch to desktop you can export from there.
Can you please confirm which export method you used and which web browser?
You can export from the browser extension: left click the icon > Account Options > Advanced > Export > LastPass CSV. (Then you might be asked to enter your Master Password again).
You can export your data while signed into your vault directly on our website: click Advanced Options > Export (a verification email is sent, open it and click on the link to continue), return to your Vault, then go to Advanced Options > Export again.
I would suggest the first method using the LastPass extension in Chrome, I have tested multiple times with my test accounts.
LastPass Free customers that have Mobile set has their device type can still sign in on the website or through the browser extension to access Account Settings and Advanced Options without having to switch to Desktop. Just dismiss the message about switching when you sign in.
There is an issue with Exporting when you do this currently, but support can enable additional switches for you until it is fixed. I added 2 more switches to your account yesterday so you could switch to Desktop and back to Mobile after the export.