IRA custodian denies investment in syndication

[Mike Dymski]

My IRA custodian denied an investment that I wanted to make in a syndication. They will not provide the reason for the denial. Their due diligence must have revealed a problem with the sponsorship group; otherwise, I believe they would have explained the reason for the denial. They approved an investment in my wife's IRA in a different fund from the same sponsor though. The sponsorship group is not exactly same in both funds though but there is material overlap. Both funds are with institutional grade sponsors with long track records. In addition, the funds were vetted by an established investment club and the club membership has invested with the sponsor numerous times over the years.

Has anyone experienced a denial before where the custodian would not provide a reason?  For the custodians out there, what would keep a custodian from providing a reason (I assume legal liability)?  It's problematic not knowing why, especially since I invested in the other fund.  And I don't know if my custodian is helping or hurting my investing.