When we use the verb expect to refer to a future probability, and the meaning of the verb expect is "to anticipate", the pattern is
expect something|someone will + {bare infinitive}
or
expect something|someone + {marked infinitive}
or
expect something|someone to be {adjective phrase}
or
expect something|someone will be {adjective phrase}
I expect the app will crash.
I expect the app to crash.
I expect the app to be buggy.
I expect the app will be buggy.
When speaking of an anticipated future possibility in the past, the pattern with will is not used.
I expected the app to crash.
I did not expect the app to crash.
I expected the app to be buggy.
I did not expect the app to be buggy.
But you can use would instead of will:
I expected the app would be buggy.
NOTE: A relatively small subset of native speakers, not all of them, use the verb expect also to mean "believe" or "suspect" and for these speakers the following non-standard pattern is available:
expect something|someone is|was {adjective phrase}
What is wrong with the dog? It's just lying there.
-- I expect it is sick.
or past tense:
What was wrong with the dog? It was just lying there.
-- I expect it was sick.