No, Curve448 is as good as can be per the public knowledge, see https://safecurves.cr.yp.to/. What one could expect given Rambus history is undisclosed patents, possibly the most efficient hardware implementation. They have been known to get their tech standardized (not disclosing IP claims) and come back at adopters with patent violation suits.
Cryptography Research patented quite a few DPA/SPA countermeasures, if there is a non obvious patent on Curve448 it will likely be one of those making it hard to make a non infringing, fast yet not vulnerable HW implementation... Given their business in licencing those countermeasure (https://www.rambus.com/security/dpa-countermeasures/licensed...), one can see their eagerness to get some curves in widely used standards as suspicious in that light.
I'm not really concerned but I also understand why one wouldn't implement anything Rambus related given their history of patent trolling...