relation of numerical error to gfortran?

Hello All, Has anyone experienced numerical errors when using NONMEM with gfortran but not intel fortran? We have a complex PKPD model which gave us strage individual fitting with NM7.5.1 (compiled by gfortran) but not NM7.4.3 (compiled with intel fortran). When using NM7.5.1, there is an unexpected & abrupt change of the time profile in some individuals, which is likely caused by the issue of numerical integration. This is a model with a large percent of BLQ, and has an extremely long run time (3 day with full parallelization). We used NOHABORT in SAEM estimation. Somehow we failed to install NM7.5.1 and PsN 5.2.6 properly on our linux cluster (CentOS) when using intel fortran. Thus no apple-to-apple comparison can be made (NM 7.5.1 by gfortran v.s. NM 7.5.1 by intel fortran). I am wondering if you have experienced cases where gfortran gave an issue but intel fortran is ok, for the same NONMEM version. The changes made in NM7.5.1 could also be related to this issue. Any thoughts or experience around this could also be very helpful. Thanks a lot for your insights Best, Tong