Question: why these ODE's hang or return unsolved in Maple 2020, but OK in 2019 and Maple 2018 ?

When I tried these ODE's in Maple 2019, and Maple 2018, they are worked (i.e. gave solutions). Now these ODE's either hang in 2020 or return unsolved. What could have caused this? On Maple 2020, under windows 10:

restart;
ode:=(x^2-1)*diff(y(x),x)^2-y(x)^2+1=0:
dsolve(ode); #hangs

restart;
ode:=(2*x^2+1)*diff(y(x),x)^2+(y(x)^2+2*x*y(x)+x^2+2)*diff(y(x),x)+2*y(x)^2+1=0:
dsolve(ode); # return unsolved

restart;
ode:=x*y(x)^2*diff(y(x),x)^3-y(x)^3*diff(y(x),x)^2+x*(x^2+1)*diff(y(x),x)-x^2*y(x):
dsolve(ode); # return unsolved

restart;
ode:=(diff(y(x),x) = (-y(x)^2+4*a*x)^3/(-y(x)^2+4*a*x-1)/y(x)):
dsolve(ode); #hangs

I noticed that in Maple 2019.2 this problem is also there. But not in Maple 2019.  So something changed from after Maple 2019.

Here is worksheet on Maple 2018 that shows these worked there. But no longer work on Maple 2020. There might be more like these but these the ones I found so far.

issue.mw