What is the difference between these sentences?
- Your app may simply get lost
- Your app may simply lost
"Lost" is an adjective. It modifies the subject of the sentence through a verb.In your second sentence there is no verb, therefore you will need to insert a verb to make the sentence grammatically correct.
You cannot shorten the sentence any more, because any alteration will changes the meaning of the sentence.
In the message "Your app may simply get lost", the action of the sentence is being performed upon the app, so if you change the sentence to make the app do the action (i.e. The app may simply lose), it completely changes the semantics of the sentence.
The first one looks grammatically correct. But its meaning depends on what you want to say: if it happened in the past, or if it's likely to happen in the future, require different structures; I think Rimmer provided a good explanation on this part.
The second one is totally incorrect. "May" is a modal verb and such category usually requires them to be followed by another verb without the "to", with the exception of "ought to" and "used to". See these examples taken from the OALD (and some added by me):
- You may go home now.
- You must find a job.
- You ought to stop smoking.
- I used to smoke but I gave up two years ago.
The word lost is the past participle of the verb lose. In the sentence “Your app may simply get lost” the verb phrase is “may simply get lost” where “get lost” is a verb structure known as a get-passive. It is a form of the passive voice that uses the verb get whereas the normal passive voice uses the verb be. (See this related question).
The second sentence “Your app may simply lost” is ungrammatical. The auxiliary verb may requires attachment to an infinitive verb phrase, and lost is a bare participle, so it cannot be used in that position.