Here the tests I have done
# TEST 1: ADD JOIN USING MEMORY FC AND TABLE
#COPY TABLE IN MEMORY
arcpy.conversion.TableToTable("HERE_DA_Bardonechia_A32_SS335_Vittoria", "memory", "HERE_DA_Bardonechia_A32_SS335_VittoriaMemory", .........)
#COPY FC IN MEMORY
arcpy.conversion.FeatureClassToFeatureClass(r"A32BardonnexOulx\StreetsA32BardonecchiaOulx", "memory", "StreetsA32BardonecchiaOulxMemory", .......)
#ADD JOIN BETWEEN MEMORY FC AND MEMORY TABLE
arcpy.management.AddJoin("StreetsA32BardonecchiaOulxMemory", "LINK_DIR_FROM", "HERE_DA_Bardonechia_A32_SS335_VittoriaMemory", "LINK_DIR", "KEEP_COMMON")
# => 37 records joined in StreetsA32BardonecchiaOulxMemory
# TEST 2: ADD JOIN USING GDB FC AND TABLE
arcpy.management.AddJoin(r"A32BardonnexOulx\StreetsA32BardonecchiaOulx", "LINK_DIR_TO", "HERE_DA_Bardonechia_A32_SS335_Vittoria", "LINK_DIR", "KEEP_COMMON")
# => 4 536 records joined in StreetsA32BardonecchiaOulx (expected result)
I get only 37 rows joined (each feature is joined only once) if I used memory FC and table.
Thanks for your help.