Could it be due to the zero constant setting?
"php.format.rules.nullConstantCasing": "lowercase"
Here are the complete settings of the PHP extension for comparison:
{
"intelliphp.inlineSuggestionsEnabled": true,
"php.completion.namingConvention": "snake_case",
"php.completion.parameters": "parentheses",
"php.docblock.classSnippet": {},
"php.format.rules.addCommaAfterLastArrayElement": true,
"php.format.rules.addCommaAfterLastCallParameter": true,
"php.format.rules.addCommaAfterLastDeclParameter": true,
"php.format.rules.alignConsecutiveAssignments": false,
"php.format.rules.alignConstants": true,
"php.format.rules.alignEnumCases": true,
"php.format.rules.alignMatchArmBodies": true,
"php.format.rules.arrayInitializersAlignKeyValuePairs": true,
"php.format.rules.arrayInitializersNewLineAfterLastElement": true,
"php.format.rules.arrayInitializersNewLineBeforeFirstElement": true,
"php.format.rules.blankLinesAfterClass": 1,
"php.format.rules.blankLinesAfterFunction": 1,
"php.format.rules.blankLinesAfterMethod": 1,
"php.format.rules.booleanConstantCasing": "lowercase",
"php.format.rules.callParametersNewLineAfterLeftParen": true,
"php.format.rules.callParametersNewLineBeforeRightParen": true,
"php.format.rules.catchOnNewLine": false,
"php.format.rules.elseOnNewLine": false,
"php.format.rules.finallyOnNewLine": true,
"php.format.rules.forStatementNewLineAfterLeftParen": true,
"php.format.rules.forStatementNewLineBeforeRightParen": true,
"php.format.rules.groupUseNewLineBeforeFirstDeclaration": true,
"php.format.rules.ifStatementNewLineAfterLeftParen": false,
"php.format.rules.ifStatementNewLineBeforeRightParen": false,
"php.format.rules.indentBraces": false,
"php.format.rules.newLineAfterImplements": true,
"php.format.rules.nullConstantCasing": "lowercase",
"php.format.rules.openBraceOnNewLineForAnonymousClasses": false,
"php.format.rules.openBraceOnNewLineForBlocks": false,
"php.format.rules.openBraceOnNewLineForTypes": false,
"php.format.rules.spaceAfterCast": true,
"php.format.rules.spaceAroundConcatenation": false,
"php.format.rules.spaceBeforeColonInControlStatements": false,
"php.format.rules.spaceBeforeParenthesesInControlStatements": true,
"php.format.rules.switchStatementNewLineAfterLeftParen": false,
"php.hover.fullname": true,
"php.inlayHints.parameters.enabled": true,
"php.inlayHints.parameters.suppressNameMatchingValue": true,
"php.inlayHints.types.return": true,
"php.inlayHints.types.variable": true,
"php.linkedEditing.variables": true,
"php.problems.excludeGitIgnore": true,
"php.problems.scope": "all",
"php.stubs": [
"*",
"imagick",
"xdebug"
],
"php.suggest.basic": true,
"php.validate.executablePath": ""
}