The phrase "are usually not apparent" is correct and usable in written English.
It can be used to describe situations or characteristics that are typically not easily seen or understood.
Example: "The underlying issues in the project are usually not apparent until the final stages of development."
Alternatives: "are often not visible" or "tend to be unclear".
Children with this illness are born with weak muscles but their disability is usually not apparent until they are beginning to walk and use their leg muscles.
When the parent is off the nest, adjacent feathers are directed over the brood patch, and it is usually not apparent.
Although RNA motifs occur recurrently and contribute in a modular fashion to RNA architecture, it is usually not apparent which bases interact and whether it is by edge-to-edge H-bonding or solely by stacking interactions.
Bucky Fuller was not the first or the last to remind people of this truth that transformation is usually not apparent to someone who does not have a broad perspective.
As the time course of kidney damage is usually not apparent, contrast media induced nephropathy (CIN) is a promising condition for this question.
The magnitude and slow kinetics of adriamycin-induced death are similar to cell death caused by virion-delivered or transfected Vpr, which is usually not apparent until 24 48 hours after initiation of the G2,M arrest [ 2, 34, 50].
The redistribution of COH-3/4 precedes that of REC-8, which is usually not apparent until late diakinesis or prometaphase I. Thus, the kleisin subunit determines both when and where a cohesin complex will be removed from chromosomes during late prophase and prometaphase.
While the symptomatology of ASD is usually not apparent until 2 years of age, an additional lag time occurs between the moment when parents become worried about their child and the time the child receives a diagnosis and is enrolled in behavioral therapy [ 15].
The knowledge gained from a generalizability study offers an informed way out of unreliability, which is usually not apparent to researchers faced with the results of common CTT reliability measures (e.g. inter-rater ICC, kappa or a Cronbach's alpha).
There are columellae (sterile structures that start at the base of the gleba and extend through it), which are usually not evident in the mature gleba, but apparent at the base of the spore sac.
