i'm having similar issue and it's super annoying i feel you. when ever i go to play ranked i get disconnected. every single time. most of the time it shows i'm loaded in at 100%. by the time i try and reconnect the game is either over, league crashed, or i just keep getting disconnected at 100% and can't join the game. it's so god damn annoying. i've gotten penalized 3 times now for 5 games each penalty. 20 minute waits per game. and the most annoying thing is that when i go to play aram during those penalty games i connect perfectly fine with zero issues. it's when i go to summoners rift ranked that all the problems are mostly occurring at. and i play 80% ranked games so league is just dead in the water for me right now and it's so frustrating. i've made 4 boards post in the last week and not a single helpful comment has been made by anyone let alone anyone at riot. i also checked my internet with the tool tip after being "afk" and it turns out my internet speed is "great" showing it's 94/100 for speed. i've been playing league since season 5 and i still love the game. but honestly i feel like riot is just shitting their pants recently. trying to push out as much content as possible to try and stay relevant. and in doing so they end up fucking up their maintenance and servers at the expense of trying to keep people as interested as possible. only problem is i don't care for half the shit they're pushing out. i just want to play league i don't care about a new aram map or pyke being released asap or an aatrox rework. i want to play league not get penalized when ever i try to play league to rank up. i do admit i play league on an older macbook pro but i've never had this many problems with league ever before in such a short amount of time. it's super annoying. 2 weeks ago i wasn't having any problems at all. this past week almost every other day i run into at least 3 bugs, crashes and other shitty things.
Something hat might help you actually is just hitting "enter" or "shift" when you have the black screen when loading in. i did have that issue about a year and a half ago. but i'm not sure if it's the same issue that i had way back when or if you're having problems more like the ones i just described. let me know. unlike riot i'm actually curious about your problems
