** Insurance marketplace Accelerant's ARX.N shares plunge 24.8% to $22.03, hitting post-IPO low

** Piper Sandler says quality of earnings weighing on ARX; slashes PT to $25 from $35

** Brokerage says ARX's relationship with private fronting company Hadron "has raised investor concerns about growth and quality of its third quality written premiums"

** Hadron is owned by ARX's private equity sponsor Altamont Capital

** Net loss ratio in ARX's underwriting business was also higher than expected, Piper Sandler says

** Morgan Stanley Research says Hadron’s growth contribution to the exchange and how other partners can grow on the platform will be a focus going forward

** 6 of 8 brokerages rate the stock "buy" or higher and 2 "hold"; median PT $33 — data compiled by LSEG

** As of last close, ARX stock up 39.5% since July debut

(Reporting by Arasu Kannagi Basil in Bengaluru)

((ArasuKannagi.Basil@thomsonreuters.com))