In this case it was webform. Webform services wouldn't load, I couldn't clear cache, clearing db caches manually wouldn't work. All I got was:
[Thu May 07 14:37:33.174757 2020] [php7:notice] [pid 2795] [client x.x.x.x:25119] Symfony\\Component\\DependencyInjection\\Exception\\ServiceNotFoundException: The service "webform_scheduled_email.manager" has a dependency on a non-existent service "webform.token_manager". in /var/www/html/www.actionfund.org/vendor/symfony/dependency-injection/Compiler/CheckExceptionOnInvalidReferenceBehaviorPass.php on line 31 #0 /var/www/html/www.actionfund.org/vendor/symfony/dependency-injection/Compiler/AbstractRecursivePass.php(60): Symfony\\Component\\DependencyInjection\\Compiler\\CheckExceptionOnInvalidReferenceBehaviorPass->processValue(Object(Symfony\\Component\\DependencyInjection\\Reference), false)\n#1 /var/www/html/www.actionfund.org/vendor/symfony/dependency-injection/Compiler/CheckExceptionOnInvalidReferenceBehaviorPass.php(28): Symfony\\Component\\DependencyInjection\\Compiler\\AbstractRecursivePass->processValue(Array, false)\n#2 /var/www/html/www.actionfund.org/vendor/symfony/dependency-injection/Compiler/AbstractRecursivePass.php(67): Symfony\\Component\\DependencyInjection\\Compiler\\CheckExceptionOnInvalidReferenceBehaviorPass->processValue(Array)\n#3 /var/www/html/www.actionfund.org/vendor/symfony/dependency-injection/Compiler/CheckExceptionOnInvalidReferenceBehaviorPass.php(28): Symfony\\Component\\DependencyInjection\\Compiler\\AbstractRecursivePass->processValue(Object(Symfony\\Component\\DependencyInjection\\Definition), true)\n#4 /var/www/html/www.actionfund.org/vendor/symfony/dependency-injection/Compiler/AbstractRecursivePass.php(60): Symfony\\Component\\DependencyInjection\\Compiler\\CheckExceptionOnInvalidReferenceBehaviorPass->processValue(Object(Symfony\\Component\\DependencyInjection\\Definition), true)\n#5 /var/www/html/www.actionfund.org/vendor/symfony/dependency-injection/Compiler/CheckExceptionOnInvalidReferenceBehaviorPass.php(28): Symfony\\Component\\DependencyInjection\\Compiler\\AbstractRecursivePass->processValue(Array, true)\n#6 /var/www/html/www.actionfund.org/vendor/symfony/dependency-injection/Compiler/AbstractRecursivePass.php(39): Symfony\\Component\\DependencyInjection\\Compiler\\CheckExceptionOnInvalidReferenceBehaviorPass->processValue(Array, true)\n#7 /var/www/html/www.actionfund.org/vendor/symfony/dependency-injection/Compiler/Compiler.php(140): Symfony\\Component\\DependencyInjection\\Compiler\\AbstractRecursivePass->process(Object(Drupal\\Core\\DependencyInjection\\ContainerBuilder))\n#8 /var/www/html/www.actionfund.org/vendor/symfony/dependency-injection/ContainerBuilder.php(789): Symfony\\Component\\DependencyInjection\\Compiler\\Compiler->compile(Object(Drupal\\Core\\DependencyInjection\\ContainerBuilder))\n#9 /var/www/html/www.actionfund.org/web/core/lib/Drupal/Core/DrupalKernel.php(1321): Symfony\\Component\\DependencyInjection\\ContainerBuilder->compile()\n#10 /var/www/html/www.actionfund.org/web/core/lib/Drupal/Core/DrupalKernel.php(902): Drupal\\Core\\DrupalKernel->compileContainer()\n#11 /var/www/html/www.actionfund.org/web/core/lib/Drupal/Core/DrupalKernel.php(477): Drupal\\Core\\DrupalKernel->initializeContainer()\n#12 /var/www/html/www.actionfund.org/web/core/lib/Drupal/Core/DrupalKernel.php(693): Drupal\\Core\\DrupalKernel->boot()\n#13 /var/www/html/www.actionfund.org/web/index.php(19): Drupal\\Core\\DrupalKernel->handle(Object(Symfony\\Component\\HttpFoundation\\Request))\n#14 {main}
Reinstall drupal wouldn't fix it (once custom modules were in). Deleting vendor and composer install wouldn't fix it. Reloading DB had no effect. None of the usual tricks worked. I was pulling my hair out.