API error responses generated by AbuseFilter and SpamBlacklist have changed, as announced here: https://lists.wikimedia.org/pipermail/mediawiki-api-announce/2019-September/000148.html (relevant task: T229539).
It appears you have special handling for the old responses. It should be updated, otherwise they will probably show a generic error message instead of a more specific one.
extensions/MobileFrontend/src/mobile.editor.overlay/AbuseFilterOverlay.js:
9: * is related to the abusefilter extension.
17: className: 'overlay abusefilter-overlay'
extensions/MobileFrontend/src/mobile.editor.overlay/AbuseFilterPanel.js:
7: * Panel that shows an error message related to the abusefilter extension.
36: readMoreMsg: mw.msg( 'mobile-frontend-editor-abusefilter-read-more' )
44: <p></p><a href="#/abusefilter" class="readmore">{{readMoreMsg}}</a>
58: this.overlayManager.add( /^\/abusefilter$/, function () {
65: msg = mw.msg( 'mobile-frontend-editor-abusefilter-warning' );
67: msg = mw.msg( 'mobile-frontend-editor-abusefilter-disallow' );
extensions/MobileFrontend/src/mobile.editor.overlay/EditorOverlayBase.js:
285: 'abusefilter-disallowed': 'extensionAbuseFilter',
extensions/MobileFrontend/src/mobile.editor.overlay/parseSaveError.js:
48: if ( /^abusefilter-warning/.test( code ) ) {
51: type: 'abusefilter',
57: } else if ( /^abusefilter-disallow/.test( code ) ) {
60: type: 'abusefilter',
66: } else if ( /^abusefilter/.test( code ) ) {
69: type: 'abusefilter',
extensions/MobileFrontend/src/mobile.editor.overlay/SourceEditorOverlay.js:
527: } else if ( data.type === 'abusefilter' ) {
extensions/MobileFrontend/tests/node-qunit/mobile.editor.overlay/EditorGateway.test.js:
152: code: 'abusefilter-warning-usuwanie-tekstu',
162: code: 'abusefilter-disallow',
172: code: 'abusefilter-something',
465: type: 'abusefilter',
489: type: 'abusefilter',
513: type: 'abusefilter',