iPhone 6s with iOS 12.4 not connecting to MacBook Pro mid2015 with macOS 10.14.6 I am using an iPhone 6s with iOS 12.4 and a MacBook Pro mid2015 with macOS 10.14.6. Since recently (I am not exactly sure when it started), I cannot charge the phone with my computer anymore. As soon as I plug the phone in, it will play the charging sound repeatedly. The right-hand side port sometimes works, the lefthand side port never works. When I connect my old iPhone 5 (using the same cable), it charges without any issues. My iPad mini 4 shows the same issue.

Sometimes the "Do you trust this computer" setting flashes on the phone and disappears before I can click anything. 

How can I fix this?

Update 1

Sometimes I get the Software Update dialogue in macOS. After approx. 2 minutes it shows the following: 



Update 2

For some reason the issue disappeared for a while but is back now. Disabling "Settings" > "Touch ID &amp; Passcode" > "USB Accessoires" seems like it makes the problem a bit less bad, but not go away.

Update 3

This is driving me crazy. I upgraded to Mojave 10.14.3 mostly to get rid of the issue. It persists. Some more random information: Before logging in (Filevault pre-boot authentication), the phone will charge fine. Only when a user account is loaded, the issue appears. The likelihood of a successful connection increases with the battery state of the iPhone. Workaround 2 in my answer below suggest that this a "Trust issue" from the iPhone's side. I suppose the solution will have to be hidden somewhere there...



What I tried so far (will update):


Reset Privacy settings on iPhone
Different (original, almost new Apple) lightning cables 
"Disable unless needed" option for USB
Remove and add "iPhone USB" in Network Settings
Change and remove Thunderbold Bridge in Network Settings
SMC reset (thanks Jack3231), PRAM reset
Upgrade to latest iOS 12.4 and MacOS 10.14.6
Workaround 1

This is the only reliable workaround for my iPhone.

I came across a similar question. The most up-voted answer lets me charge my phone. However, I consider it rather a workaround than a solution.

Launch "Activity Monitor" > select the usbd process > click the cross icon in the top left corner > select "Force Quit". Sometimes the process has to be repeated once.

Unfortunately, this workaround does not work for my iPad mini 4, which will say Not Charging after quitting usbd.

Workaround 2

This is a weird one... I noticed that sometimes the Trust this Computer? dialogue appeared for a split second. However, it did not appear long enough to actually click  the Trust button (left button). After playing whack-a-mole for a while, I accidentally opened the Calculator App. There I was able to catch the dialogue and then I was asked to enter my Passcode. After repeating this twice it worked even after rebooting the computer. The phone will work randomly for a while.