If ALIAS-Maple returns a wrong result the most probable reason is that the theoretical system of expression has not been correctly translated into a C++ interval equivalent. This may occur if the expression involves numerical values and the value of the Maple Digits variable has a low value (by default the value is 10). With a too low value there may be a round-off of any numerical values that may indeed cause a solving problem. Hence Digits and the `ALIAS/digits` of ALIAS-Maple should be set to a large value (typically 40).
You must also be careful with expression involving rational numbers that may be not translated correctly in C++ (for example 3/9 is usually quite different from 3./9.).