In my Star system, there are 7 planets. Right now under my own faction, I am controlling 5 planets and 1 mining station in the same star system and 1 Coronal Hypershunt in another star system.
If I try to colonize another planets in the same system with my other 5 colonies. I will get this new colony is inaccessible to my market and this error message. The 6th colonies can't complete the Spaceport and will be stuck like this forever.
If I use "Abandon planet" on the 6th colony, the game will random decolonize one of the 5 planets I am controlling.
Spoiler
"SBTM" (Slightly Better Tech-Mining),
"yunruindustries",
"pantera_ANewLevel40",
"darkborderman.addstablelocations",
"advanced_gunnery_control_dbeaa06e",
"A_S-F",
"Cryo_but_better",
"aod_vos",
"aotd_vok",
"aptlysimplehullmods",
"auto_continue_inator",
"lw_autosave",
"timid_admins",
"BVH",
"better_variants",
"BSC",
"bc",
"HMI_brighton",
"ORK",
"CaptainsLog",
"carrierui",
"CFT",
"CJHM",
"Csp",
"combatactivators",
"chatter",
"timid_commissioned_hull_mods",
"lw_console",
"Toaster_deciv",
"DetailedCombatResults",
"diableavionics",
"edshipyard",
"EmergentThreats_Vice",
"EmergentThreats_IX_Revival",
"lyr_ehm",
"FPE",
"Goat_Aviation_Bureau",
"GrandColonies",
"GMDA",
"HMI_SV",
"HMI",
"hostileIntercept",
"sun_hyperdrive",
"illustrated_entities",
"IndEvo",
"Imperium",
"timid_xiv",
"JYD",
"kyeltziv",
"lost_sector",
"LTA",
"largerZoomOut",
"lw_lazylib",
"ArkLeg",
"lobster_proliferation",
"logisticsNotifications",
"luddenhance",
"lunalib",
"exshippack",
"wisp_magicAchievementsVanillaPack",
"MagicLib",
"Mayasuran Navy",
"dp_mnemonic_utils",
"MoreBarMissions",
"more_hullmods",
"MoreMilitaryMissions",
"more_player_names",
"more_procgen_names",
"more_ship_names",
"ness_saw",
"wisp_NeutrinoDetectorMkII",
"nexerelin",
"sun_nomadic_survival",
"objects_analysis",
"ObviousNeutron",
"officerExtension",
"oas",
"wisp_perseanchronicles",
"PAGSM",
"planet_search",
"playerbounty",
"portrait_changer",
"progressiveSMods",
"pt_qolpack",
"assortment_of_things",
"refitfilters",
"RetroLib",
"roider",
"rotcesrats",
"scalartech",
"scan_those_gates",
"SCY",
"SEEKER",
"swp",
"Sound_&_Music_replacer_by_GanzolinHair",
"speedUp",
"$tarmapR",
"sun_starship_legends",
"stelnet",
"StopGapMeasures3",
"superweapons",
"timid_supply_forging",
"supportships",
"System_Marker",
"tahlan",
"Terraforming & Station Construction",
"terraformingmadeeasy",
"Tesseract_prototype",
"knights_of_ludd",
"star_federation",
"timid_tmi",
"TORCHSHIPS",
"TTSC",
"underworld",
"US",
"vic",
"variants_lib",
"vayrashippack",
"TouchOfVanilla_vri",
"whichmod",
"XhanEmpire",
"yunrucore",
"astroidships",
"prvextra",
"prvlib",
"prvrb",
"prv",
"shaderLib",
"Rouge_Redstar",
"KFM3",
"KGT6",
"KGT2"