Limited number of processes

Question

I have virtual server (AWS EC2 instance c5a.4xlarge) with Ubuntu 20.04 for running Playwright scripts. I want to execute a lot of instances of the script, but something restricts it. More than half of the server's resources are available, but I cannot launch more than a certain number of running instances.

I tried to increase limits by adding following lines in /etc/security/limits.conf:

*    soft     sigpending     12701300
*    hard     sigpending     12701300
ubuntu   soft     sigpending     12701300
ubuntu   hard     sigpending     12701300
*    soft     memlock     6553600
*    hard     memlock     6553600
ubuntu   soft     memlock     6553600
ubuntu   hard     memlock     6553600
*    soft     nofile     102400
*    hard     nofile     102400
ubuntu   soft     nofile     102400
ubuntu   hard     nofile     102400
*    soft     nproc     12701300
*    hard     nproc     12701300
ubuntu   soft     nproc     12701300
ubuntu   hard     nproc     12701300
*    soft     stack          819200
*    hard     stack          819200
ubuntu   soft     stack      819200
ubuntu   hard     stack      819200

ulimit -a
core file size          (blocks, -c) 0
data seg size           (kbytes, -d) unlimited
scheduling priority             (-e) 0
file size               (blocks, -f) unlimited
pending signals                 (-i) 12701300
max locked memory       (kbytes, -l) 6553600
max memory size         (kbytes, -m) unlimited
open files                      (-n) 102400
pipe size            (512 bytes, -p) 8
POSIX message queues     (bytes, -q) 819200
real-time priority              (-r) 0
stack size              (kbytes, -s) 819200
cpu time               (seconds, -t) unlimited
max user processes              (-u) 12701300
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited

But I still cannot launch more instances.

UPDATED DETAILS

I can launch around 40 Playwright instances (headless: false). CPU is loaded by ~15%, RAM ~ 25%. When I try to launch more it usually throws 2 errors:

Error 1 - frequent one

(node:84194) UnhandledPromiseRejectionWarning: browserType.launch: Protocol error (Browser.getVersion): Target closed.
=========================== logs ===========================
<launching> /home/ubuntu/.cache/ms-playwright/chromium-815036/chrome-linux/chrome --disable-background-networking --enable-features=NetworkService,NetworkServiceInProcess --disable-background-timer-throttling --disable-backgrounding-occluded-windows --disable-breakpad --disable-client-side-phishing-detection --disable-component-extensions-with-background-pages --disable-default-apps --disable-dev-shm-usage --disable-extensions --disable-features=TranslateUI,BlinkGenPropertyTrees,ImprovedCookieControls,SameSiteByDefaultCookies,LazyFrameLoading --disable-hang-monitor --disable-ipc-flooding-protection --disable-popup-blocking --disable-prompt-on-repost --disable-renderer-backgrounding --disable-sync --force-color-profile=srgb --metrics-recording-only --no-first-run --enable-automation --password-store=basic --use-mock-keychain --user-data-dir=/tmp/playwright_chromiumdev_profile-5Vv8kA --remote-debugging-pipe --no-sandbox --proxy-server=http://91.206.68.101:52068 --no-startup-window
<launched> pid=85115
[err] Maximum number of clients reached[85115:85115:1030/092321.045583:ERROR:browser_main_loop.cc(1434)] Unable to open X display.
============================================================
Note: use DEBUG=pw:api environment variable and rerun to capture Playwright logs.
    at Connection.sendMessageToServer (/home/ubuntu/projectDir/node_modules/playwright-chromium/lib/client/connection.js:69:15)
    at Proxy.<anonymous> (/home/ubuntu/projectDir/node_modules/playwright-chromium/lib/client/channelOwner.js:54:53)
    at /home/ubuntu/projectDir/node_modules/playwright-chromium/lib/client/browserType.js:62:73
    at BrowserType._wrapApiCall (/home/ubuntu/projectDir/node_modules/playwright-chromium/lib/client/channelOwner.js:80:34)
    at BrowserType.launch (/home/ubuntu/projectDir/node_modules/playwright-chromium/lib/client/browserType.js:53:21)
    at MyScript.initBrowser (/home/ubuntu/projectDir/scripts/myscript.js:115:33)
    at MyScript.start (/home/ubuntu/projectDir/scripts/myscript.js:44:14)
    at processTicksAndRejections (internal/process/task_queues.js:93:5)
(Use `node --trace-warnings ...` to show where the warning was created)
(node:84194) 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: 2)
(node:84194) [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.

Error 2 - rare one

projectDir/node_modules/playwright-chromium/lib/client/connection.js:138
            throw new Error(`Cannot find parent object ${parentGuid} to create ${guid}`);
            ^
Error: Cannot find parent object BrowserContext@542efe1178d54357c723ec96e9394def to create Frame@38a1562630571f41c86fea49af0a4b24
    at Connection._createRemoteObject (projectDir/node_modules/playwright-chromium/lib/client/connection.js:138:19)
    at Connection.dispatch (projectDir/node_modules/playwright-chromium/lib/client/connection.js:105:18)
    at Immediate.<anonymous> (projectDir/node_modules/playwright-chromium/lib/inprocess.js:40:85)
    at processImmediate (internal/timers.js:461:21)