The phrase "are often not sufficient" is correct and usable in written English.
It can be used when discussing situations where something does not meet the necessary requirements or standards frequently.
Example: "While these measures are helpful, they are often not sufficient to address the underlying issues."
Alternatives: "are frequently inadequate" or "are commonly insufficient."
Natural filtration mechanisms are often not sufficient during high discharge events in the river.
However, for complex materials like amorphous or nano-structured solids the given values are often not sufficient for a proper characterization.
However the measurements usually made in these analyses are often not sufficient to reliably determine many fluxes that are distributed between different subcellular compartments of eukaryotic cells.
Likewise, although correlative field studies may be useful for generating hypotheses about system drivers, they are often not sufficient to resolve causally important processes in complex hydrologic systems with multiple limiting factors or nonlinearities.
This is not to say they are not important, of course–just that alone, without attention to drivers of biodiversity decline and their relationship to the surrounding land, they are often not sufficient.
However, the results of these studies are often not sufficient for long-term projections and extrapolations to large spatial scales especially for unprecedented environmental conditions, which require both the identification and understanding of key underlying processes.
Pushing the stern sideways is tantamount to changing the direction of the hull, but this expedient is often not sufficient for low-speed maneuvering.
In some cases, your advisor will already have approvals in place for a larger project, but this is often not sufficient for the MedScholars application since MedScholars requires approval specifically including your name and project.
Limit analysis is often not sufficient for a full structural analysis under seismic loads, but it can be profitably used in order to obtain a simple and fast estimation of collapse loads.
