Same here for me. Tools were working till couple of days with on/off switch, but started appearing greyed out.
Previously it was showing me WRITE and disabled, but managed to remove WRITE by adding annotation JSON as below
annotations: {
readOnlyHint: true,
openWorldHint: false
}
But tools disabled / grayed out issue still persists.
Request to Open AI team to inspect issue from their back-end and resolve this, as the same tools are working perfectly in Claude AI. It will be nice to have custom MCP support in ChatGPT too, being preferred choice of end-users.