Can' re-start world with 21s06a

w2106a server can't reopen world created in w2106a. Log says : [11:31:28] [main/INFO]: Environment: authHost='https://authserver.mojang.com', accountsHost='https://api.mojang.com', sessionHost='https://sessionserver.mojang.com', servicesHost='https://api.minecraftservices.com', name='PROD'
[11:31:28] [main/INFO]: Loading of old worlds is temporarily disabled.