(node:21216) UnhandledPromiseRejectionWarning: Error: Cannot find module 'ajv/dist/compile/codegen'
loader.js:815 Function.Module._resolveFilename internal/modules/cjs/loader.js:815:15
loader.js:667 Function.Module._load internal/modules/cjs/loader.js:667:27
loader.js:887 Module.require internal/modules/cjs/loader.js:887:19
helpers.js:74 require internal/modules/cjs/helpers.js:74:18
typeof.js:3 Object. [front]/[mini-css-extract-plugin]/[ajv-keywords]/dist/definitions/typeof.js:3:19
loader.js:999 Module._compile internal/modules/cjs/loader.js:999:30
loader.js:1027 Object.Module._extensions..js internal/modules/cjs/loader.js:1027:10
loader.js:863 Module.load internal/modules/cjs/loader.js:863:32
loader.js:708 Function.Module._load internal/modules/cjs/loader.js:708:14
loader.js:887 Module.require internal/modules/cjs/loader.js:887:19
(node:21216) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). To terminate the node process on unhandled promise rejection, use the CLI flag --unhandled-rejections=strict (see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 1)
(node:21216) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.
I just hit the same error several times recently. In my case the error was based on ajv-keywords and ajv-formats plugin incompatibility with node js 8 and 12 (legacy project).
To analyse the problem, you can always use the npm ls ajv command, to see, which module try to use something incompatible.
Personally, I spent days to figure out the right combination for ajv schema, node and ajv plugins to make them work together properly.
(In my case, I used ajv 6.4.x, what I had to downgrade to 6.12, then I used ajv-keywords@3.5.1 and ajv-formats@1.5.1 which I had to dowgnrade to 3.0 and 1.4)