In our CRM 2016 upgrade we have uncovered 3 bugs.
1) Unable to go offline, error relating to generating BCP file.
In our database which is an older install of CRM we have a timestamp around the 8 000 000 000 mark.
When creating the BCP header file it tries to convert that timestamp to a 32 bit integer which creates an overflow exception. It seems older versions of CRM ignored this error and continued anyway.
Microsoft has now released a hotfix for this which now handles 64bit timestamps.
2) IFrames stripping out parameters relating to reporting services parameters when set via JS or form designer with Pass record type code etc ticked.
The only way around this bug so far that we have found is to upload the report into CRM and using JS set a relative URL!
3) Cannot find X method when deactivating a record
It seems when you deactivate a record it can try to call methods from a previously viewed form in the onload, the work around was to include the library from the other form in a form you are likely to be using in sequence, for example contracts and contract lines.