Sry, it seems that with ATDD+ new Drones, the Nexerelin invasion option would disappear. Though I haven't tried with ATDD+ Vanilla enabled. But I can confirm it's ATDD+ new Drones incurred this issue. Here's the screenshot and my enabled_mods.json.
{"enabledMods": [
"PAGSM",
"$$$_DakkaHolics_sprites",
"$$$_trailermoments",
"pantera_ANewLevel30R",
"adversary",
"all_the_domain_drones+NewDrones",
"anotherportraitpack",
"timid_admins",
"better_deserving_smods",
"istl_dassaultmikoyan",
"diableavionics",
"fast_engine_rendering",
"fleet_journal",
"sun_hyperdrive",
"illustrated_entities",
"IndEvo",
"timid_xiv",
"lw_lazylib",
"leadingPip",
"mag_protect",
"MagicLib",
"Mayasuran Navy",
"more_hullmods",
"ness_saw",
"wisp_NeutrinoDetectorMkII",
"nexerelin",
"officerExtension",
"ORA",
"pt_qolpack",
"roider",
"tahlan_scalartech",
"scan_those_gates",
"SCY",
"SEEKER",
"swp",
"mayu_specialupgrades",
"speedUp",
"stelnet",
"alcoholism",
"timid_supply_forging",
"tahlan",
"Terraforming & Station Construction",
"US",
"vic",
"whichmod",
"XhanEmpire",
"mir_np",
"shaderLib",
"zzz_DakkaHolics"
]}