Crashes when adding folders

As of latest next, attempting to add a resource folder seems to consistently crash SRB2, when done via UZB or command line.

Through UZB, I get this crash:

Crash 1

Error occurred on Monday, July 31, 2023 at 10:44:20.

srb2win_next.exe caused an Access Violation at location 005E929B in module srb2win_next.exe Reading from location 00000008.

Registers: eax=00000000 ebx=424f83ef ecx=07c05f48 edx=00000005 esi=07e7e63c edi=00000007 eip=005e929b esp=0549faa0 ebp=0549fe18 iopl=0 nv up ei ng nz ac pe cy cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00210293

AddrPC Params 005E929B 00000000 0040504F 0074E8FC srb2win_next.exe!W_InitFile 0040504F 0074E8FC 0074E8DD 00000002 srb2win_next.exe!SDL_main 0040504F 00000000 00000000 00000000 srb2win_next.exe!SDL_main

Through command line, I get this instead:

Crash 2

Error occurred on Monday, July 31, 2023 at 10:48:09.

srb2win_next.exe caused an Access Violation at location 005CE862 in module srb2win_next.exe Reading from location 00000008.

Registers: eax=00000000 ebx=00000006 ecx=00000000 edx=00000000 esi=00000000 edi=07f305cd eip=005ce862 esp=0549f6a0 ebp=0000001c iopl=0 nv up ei pl nz na po nc cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00210206

AddrPC Params 005CE862 07F305CD 00000000 00000019 srb2win_next.exe!R_GetFlatNumForName 00565B8C 00000007 00000007 00000000 srb2win_next.exe!P_InitPicAnims 005CE79F 00000007 00000010 00004831 srb2win_next.exe!R_LoadTexturesPwad 00552A9F 052276A0 00000000 00000000 srb2win_next.exe!P_LoadAddon 00560668 077DD47C 077DD490 00000000 srb2win_next.exe!P_AddWadFile 0048F810 00000F7F 0549037F 0549FD50 srb2win_next.exe!COM_BufExecute 004461EF D3C7951E 3FE9C3F2 0549FD50 srb2win_next.exe!TryRunTics 0049D471 00000001 00000000 00010000 srb2win_next.exe!I_UpdateTime 00437DFB 00000000 00000000 00000000 srb2win_next.exe!D_SRB2Loop

The weird thing here is that my folder resource doesn't add any flats nor defines an animated flat.

Adding a folder while already in-game does work, but attempting to load any addon after that will crash as well.