I had a problem very similar to yours, but worse. I talked to support for a very long time to no avail. Some said it was an internet problem and i could do nothing about it. They were wrong.
What was causing my issue? Apparently Malwarebytes or Hitmanpro.alert. After uninstalling both of the antimalware/anti-keylogger programs it fixed. So, try uninstalling your antiviruses. I didn't think this was ever the problem because i NEVER had this problem before while having these programs. It just magically happened, and I dealt with it for years.
My issues were:
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Client wouldn't launch/open. Had to run it as admin to get it to open. Eventually, running as admin wouldn't even work. Often times it would say the client needed to repair itself. Restarting my computer caused it to fix very temporarily.
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In-game load screen wouldn't pop up, instead, bringing me back to the client with "reconnect" as an option. I'd sometimes have to repetitively spam "reconnect" until finally, it loaded in.
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When load screen did open, sometimes it would never actually load into the game. It would just stay in the load screen, stuck until I ended its process in task manager. This would keep happening, leading to me being unsure as to whether or not the game actually started.
TL;DR - try uninstalling your antiviruses, all of them. I had the same issue except mine started like yours and got progressively worse. Uninstalling malwarebytes and hitmanpro.alert fixed it after years of dealing with this similar issue. Restart PC after uninstalling them.
Edit: saw it was Avast thing. Yeah... I still went through these troubles with other antivirus/antimalware programs.