The phrase "are still several problems" is correct and usable in written English.
It can be used when discussing ongoing issues or challenges that have not yet been resolved.
Example: "Despite the progress we've made, there are still several problems that need to be addressed before the project can be completed."
Alternatives: "remain several issues" or "continue to be several challenges".
There are still several problems that bedevil the area.
There are still several problems we have not found solutions over decades/centuries.
No wonder Nokia and other mobile-infrastructure manufacturers are keeping a close eye on ad hoc networking.But there are still several problems to overcome.
However, there are still several problems in these local thresholding methods.
However, there are still several problems in the dual-QDs-labeled LFS designed in this paper.
There are still several problems which will hinder our future development of MEMS devices.
However, there are still several notable problems in the determination of the drug loading content (DLC) and the drug loading efficiency (DLE) of the drug delivery vehicles.
The presented review shows that the collision-free trajectory planning in space robotics is a very active field of studies, but there are still several open problems that need to be solved before the proposed methods could be applied during on-orbit servicing, active debris removal and on-orbit assembly of large structures.
Although we have provided the main basic elements via the LDP and finite-dimensional approximations, there are still several very interesting open problems.
It's a credit to Hangar 13's world building that despite these problems there are still several hours of entertainment to be found in cruising around shooting goons, or pulling off a car chase through Downtown with a dozen cop cars on your tail with "Born to be Wild" blaring out of the stereo.
Despite the success of individual design solutions in addressing health problems, there are still several barriers to institutionalizing a greater integration of design and healthcare.
