"complex and longstanding" is a correct and usable phrase in written English.
You can use it to describe a problem or issue that has been around for a long time and is difficult to solve. Example: The dispute between the two countries is a complex and longstanding one, with a history of unresolved issues.
The problems are complex and longstanding.
While the UK's decision to leave the EU has complex and longstanding roots, it is undeniably part of this trend.
Much of Eastern Ontario, including North Frontenac, is the subject of a complex and longstanding land claim launched by the Algonquin Indian tribe.
Even a treatment period of a year may have been too short for participating patients who had long histories of heavy drug and alcohol misuse (often characterised by polysubstance use), complex and longstanding mental health problems, and low levels of social functioning and support.
We must therefore confront "the powerful narrative that weaves together conflicts from across the globe, presenting the west's response to varied and complex issues, from longstanding disputes such as Israel/Palestine and Kashmir to more recent events, as evidence of an across-the-board determination to undermine and humiliate Islam worldwide".
"It is going to say, 'In the future, don't make things parkland, because it removes your options in a complex and difficult city.' " By longstanding tradition, the Legislature almost never approves the use of parks for other purposes unless the legislators who represent the site give their consent.
The United States and Egyptian militaries have close and longstanding ties.
The trend is national and longstanding.
The HS1,2A allele *2 associates with early and longstanding RA.
The origin and diversification of novel traits are central and longstanding issues in evolutionary biology [ 1].
Measures of general health, hospital admissions, and longstanding illness showed similar patterns.
