如果在服务器上无法使Angular 7 - Service Worker PWA + SSR正常工作，可能有以下几个原因：

1. 缺少Angular的依赖项：确保已安装了必要的依赖项。在项目根目录下运行以下命令：

npm install

2. 错误的服务器配置：检查服务器配置是否正确。确保已启用了Service Worker和SSR相关的配置选项。

3. 缺少HTTPs支持：Service Worker要求在HTTPS环境下运行。在本地开发环境中，可以使用自签名证书来启用HTTPS。在服务器上，确保已正确配置和启用HTTPS。

以下是一个基本的Angular 7 - Service Worker PWA + SSR的示例代码：

1. 确保在angular.json文件中启用了Service Worker和SSR选项：

"projects": {
  "your-project-name": {
    "architect": {
      "build": {
        "options": {
          "serviceWorker": true
        }
      },
      "server": {
        "builder": "@angular-devkit/build-angular:server",
        "options": {
          "outputPath": "dist/server",
          "main": "src/main.server.ts"
        }
      }
    }
  }
}

2. 在src/main.ts文件中注册Service Worker：

import { enableProdMode } from '@angular/core';
import { platformBrowserDynamic } from '@angular/platform-browser-dynamic';
import { environment } from './environments/environment';

import { AppModule } from './app/app.module';
import { ServiceWorkerModule } from '@angular/service-worker';
import { environment as swEnvironment } from './sw-env';

if (environment.production) {
  enableProdMode();
}

platformBrowserDynamic().bootstrapModule(AppModule)
  .then(() => {
    if (swEnvironment.production) {
      ServiceWorkerModule.register('/ngsw-worker.js');
    }
  })
  .catch(err => console.log(err));

3. 在src/main.server.ts文件中启用SSR：

import 'zone.js/dist/zone-node';

import { enableProdMode } from '@angular/core';
import { renderModuleFactory } from '@angular/platform-server';
import { provideModuleMap } from '@nguniversal/module-map-ngfactory-loader';

import * as express from 'express';
import { readFileSync } from 'fs';
import { join } from 'path';

enableProdMode();

const app = express();
const PORT = process.env.PORT || 4000;
const DIST_FOLDER = join(process.cwd(), 'dist');
const { AppServerModuleNgFactory, LAZY_MODULE_MAP } = require('./server/main');

app.engine('html', (_, options, callback) => {
  const template = readFileSync(join(DIST_FOLDER, 'browser', 'index.html')).toString();
  const { AppServerModule, LAZY_MODULE_MAP } = options.bundle;
  renderModuleFactory(AppServerModuleNgFactory, {
    document: template,
    url: options.req.url,
    extraProviders: [
      provideModuleMap(LAZY_MODULE_MAP)
    ]
  }).then(html => {
    callback(null, html);
  });
});

app.set('view engine', 'html');
app.set('views', join(DIST_FOLDER, 'browser'));

app.get('*.*', express.static(join(DIST_FOLDER, 'browser')));

app.get('*', (req, res) => {
  res.render('index', { req, providers: [{ provide: APP_BASE_HREF, useValue: req.baseUrl }] });
});

app.listen(PORT, () => {
  console.log(`Node server listening on http://localhost:${PORT}`);
});

请根据你的项目进行适当的调整，并确保您的服务器配置正确。