I think you are hitting known issues... We are having same problem with critical authentication.  Meraki MS versions have same problem from MS16.9 version but this problem stiil continue and not resolve..   RADIUS communications may not recover after an initial failure when Critical Auth is enabled   We do not understand why such an important problem has not been solved yet.. ... View more

Hi , Can you take a packet capture on your cloud RADIUS server ? Can you see those fragments ?   Your radius server should perform IP reassembly unless it never receives the fragments ( a.k.a dropped in transit ) ... View more