Timing Corner

I'm not sure if that solution is still valid, but the fitter generally does optimize for all corners. If it constantly failed at one corner and didn't try, we'd have designs failing left and right. Note that I am talking more about hold failures, where it adds delay, which is a tricky thing to do since you want to add as little delay as possible that meets timing. For setup, you work on improving the paths as much as you can, and if it happens to be a failure in the middle corner, so be it.

What type of failures are you seeing? As much detail as possible, please. Setup, hold recovery or removal? Is there anything special about it, like it's between a XCVR and fabric register, or DSP to DSP, or something like that? Is there any clock skew? Etc. Maybe we can find a manual workaround.