This issue isn't specific to phpbb 3.3, I also had the problem with phpbb 3.2- but it seems to be getting worse.
I keep getting a Forbidden message when I visit pages of my forum. I'm locked out for 5-10 minutes and then it returns to normal.
I don't have the problem with my main Joomla site, I can view that without any issues. It is only phpbb.
My forum users also get this from time to time. It is not just me as admin.
It is not browser related. I'm locked out with Internet Explorer, Microsoft Edge and Firefox.
I can visit the forum during a Forbidden period when I use my Samsung phone.
I've search this forum for answers, but none seem to apply to my situation.
What could be causing this and what can I do to fix it? Please help, it is driving me to insanity