Custom Fields vanish

Hello,

This was working fine just a few days ago, now I'm having a problem that seems very similar to this issue: https://support.metabox.io/topic/major-problem-specific-custom-field-group-vanishes/

Latest WP, latest MB. Clean WP install, only MB and MB AIO activated. I go to Custom Fields, click Edit and see the settings flash for a moment, then disappear. Trashed and deleted all fields, clicked New and same thing. Console reports the following errors:

GET https://xxx.cloud.bunnyroute.com/wp-json/mbb/settings-controls 403
u @ app.js?ver=4.1.13:1
(anonymous) @ app.js?ver=4.1.13:13
$r @ react-dom.min.js?ver=17.0.1:9
unstable_runWithPriority @ react.min.js?ver=17.0.1:9
xn @ react-dom.min.js?ver=17.0.1:9
Qr @ react-dom.min.js?ver=17.0.1:9
(anonymous) @ react-dom.min.js?ver=17.0.1:9
h @ react.min.js?ver=17.0.1:9
ne.port1.onmessage @ react.min.js?ver=17.0.1:9
app.js?ver=4.1.13:1
GET https://xxx.cloud.bunnyroute.com/wp-json/mbb/field-types 403
u @ app.js?ver=4.1.13:1
(anonymous) @ app.js?ver=4.1.13:1
$r @ react-dom.min.js?ver=17.0.1:9
unstable_runWithPriority @ react.min.js?ver=17.0.1:9
xn @ react-dom.min.js?ver=17.0.1:9
Qr @ react-dom.min.js?ver=17.0.1:9
(anonymous) @ react-dom.min.js?ver=17.0.1:9
h @ react.min.js?ver=17.0.1:9
ne.port1.onmessage @ react.min.js?ver=17.0.1:9
app.js?ver=4.1.13:1
GET https://xxx.cloud.bunnyroute.com/wp-json/mbb/field-categories 403
u @ app.js?ver=4.1.13:1
(anonymous) @ app.js?ver=4.1.13:1
$r @ react-dom.min.js?ver=17.0.1:9
unstable_runWithPriority @ react.min.js?ver=17.0.1:9
xn @ react-dom.min.js?ver=17.0.1:9
Qr @ react-dom.min.js?ver=17.0.1:9
(anonymous) @ react-dom.min.js?ver=17.0.1:9
h @ react.min.js?ver=17.0.1:9
ne.port1.onmessage @ react.min.js?ver=17.0.1:9
react-dom.min.js?ver=17.0.1:9 TypeError: t.map is not a function
at app.js?ver=4.1.13:13:69968
at ct (react-dom.min.js?ver=17.0.1:9:43430)
at Bt (react-dom.min.js?ver=17.0.1:9:50249)
at Ut (react-dom.min.js?ver=17.0.1:9:49583)
at Ft (react-dom.min.js?ver=17.0.1:9:49241)
at os (react-dom.min.js?ver=17.0.1:9:114369)
at Ur (react-dom.min.js?ver=17.0.1:9:77643)
at Ir (react-dom.min.js?ver=17.0.1:9:77571)
at Dr (react-dom.min.js?ver=17.0.1:9:77434)
at Pr (react-dom.min.js?ver=17.0.1:9:74429)
rr @ react-dom.min.js?ver=17.0.1:9
t.callback @ react-dom.min.js?ver=17.0.1:9
An @ react-dom.min.js?ver=17.0.1:9
ir @ react-dom.min.js?ver=17.0.1:9
Br @ react-dom.min.js?ver=17.0.1:9
unstable_runWithPriority @ react.min.js?ver=17.0.1:9
xn @ react-dom.min.js?ver=17.0.1:9
Ar @ react-dom.min.js?ver=17.0.1:9
Pr @ react-dom.min.js?ver=17.0.1:9
(anonymous) @ react-dom.min.js?ver=17.0.1:9
unstable_runWithPriority @ react.min.js?ver=17.0.1:9
xn @ react-dom.min.js?ver=17.0.1:9
Nn @ react-dom.min.js?ver=17.0.1:9
_n @ react-dom.min.js?ver=17.0.1:9
Er @ react-dom.min.js?ver=17.0.1:9
Rt @ react-dom.min.js?ver=17.0.1:9
Promise.then (async)
(anonymous) @ app.js?ver=4.1.13:13
$r @ react-dom.min.js?ver=17.0.1:9
unstable_runWithPriority @ react.min.js?ver=17.0.1:9
xn @ react-dom.min.js?ver=17.0.1:9
Qr @ react-dom.min.js?ver=17.0.1:9
(anonymous) @ react-dom.min.js?ver=17.0.1:9
h @ react.min.js?ver=17.0.1:9
ne.port1.onmessage @ react.min.js?ver=17.0.1:9

Thank you!