OSX kbfs input/output errors in team folder

Hello,

using one of our team drives recently became unbearably slow, with reports of "input/output errors" on many files.

I could find that in my local kbfs logs:

```
2019-08-30T12:31:02.059835+02:00 ▶ [WARN kbfs(BSR) bserver_remote.go:421] 1281 Get id=02240c8ee01eaf0bc0b2cb4a937df454fcf4c044ef9cf76af4ddcc88846e12470c tlf=69748b4b9f22c081b9c88eaecc0c1e26 context=Context{Creator: b341fc29dae1b491ef71b9fc0ff9f724} sz=0 err=Server: block does not exist [tags:FID=Jn92wuWf52Ji6yDF9CPNuw]
2019-08-30T12:31:02.059965+02:00 ▶ [DEBU kbfs block_retrieval_queue.go:621] 1282 Couldn't get block BlockPointer{ID: 02240c8ee01eaf0bc0b2cb4a937df454fcf4c044ef9cf76af4ddcc88846e12470c, KeyGen: 11, DataVer: 1, Context: Context{Creator: b341fc29dae1b491ef71b9fc0ff9f724}, DirectType: direct}: Server: block does not exist [tags:FID=Jn92wuWf52Ji6yDF9CPNuw]
2019-08-30T12:31:02.060153+02:00 ▶ [WARN kbfs(FBO 69748b4b) folder_branch_ops.go:3128] 1283 Got unexpected read error on a synced TLF: Server: block does not exist [tags:FID=Jn92wuWf52Ji6yDF9CPNuw]
2019-08-30T12:31:02.060274+02:00 ▶ [DEBU kbfs(FBO 69748b4b) folder_branch_ops.go:3445] 1284 [duration=193.960782ms] Lookup NodeID(0xc436fd2000) tenant-song done: NodeID(nil) Server: block does not exist [tags:FID=Jn92wuWf52Ji6yDF9CPNuw]
2019-08-30T12:31:02.060319+02:00 ▶ [DEBU kbfs(kbfsfuse) dir.go:553] 1285 Server: block does not exist [tags:FID=Jn92wuWf52Ji6yDF9CPNuw]
2019-08-30T12:31:02.187541+02:00 ▶ [WARN kbfs(BSR) bserver_remote.go:421] 1286 Get id=02240c8ee01eaf0bc0b2cb4a937df454fcf4c044ef9cf76af4ddcc88846e12470c tlf=69748b4b9f22c081b9c88eaecc0c1e26 context=Context{Creator: b341fc29dae1b491ef71b9fc0ff9f724} sz=0 err=Server: block does not exist [tags:FID=2XHpZFBLt8SaT-jiUHJ33w]
2019-08-30T12:31:02.187700+02:00 ▶ [DEBU kbfs block_retrieval_queue.go:621] 1287 Couldn't get block BlockPointer{ID: 02240c8ee01eaf0bc0b2cb4a937df454fcf4c044ef9cf76af4ddcc88846e12470c, KeyGen: 11, DataVer: 1, Context: Context{Creator: b341fc29dae1b491ef71b9fc0ff9f724}, DirectType: direct}: Server: block does not exist [tags:FID=2XHpZFBLt8SaT-jiUHJ33w]
2019-08-30T12:31:02.187821+02:00 ▶ [WARN kbfs(FBO 69748b4b) folder_branch_ops.go:3128] 1288 Got unexpected read error on a synced TLF: Server: block does not exist [tags:FID=2XHpZFBLt8SaT-jiUHJ33w]
2019-08-30T12:31:02.187891+02:00 ▶ [DEBU kbfs(FBO 69748b4b) folder_branch_ops.go:3445] 1289 [duration=127.229799ms] Lookup NodeID(0xc436fd2000) tenant-song done: NodeID(nil) Server: block does not exist [tags:FID=2XHpZFBLt8SaT-jiUHJ33w]
2019-08-30T12:31:02.188039+02:00 ▶ [DEBU kbfs(kbfsfuse) dir.go:553] 128a Server: block does not exist [tags:FID=2XHpZFBLt8SaT-jiUHJ33w]
```

has some block disappeared from server storage ? Is there anyway we can recover those blocks ? (we have backups)

I tried to use keybase log send to provide some more info but:

```
This command will send recent keybase log entries to keybase.io
for debugging purposes only.

These logs don’t include your private keys, encrypted data or file names,
but they will include metadata Keybase normally can't read
(like file sizes and git repo names), for debugging purposes.

Continue sending logs to keybase.io? (type 'YES' to confirm): YES
▶ INFO ignoring UI logs: GUI main process wasn't found
▶ ERROR API network error: Post https://api-0.core.keybaseapi.com/_/api/1.0/logdump/send.json: net/http: request canceled (Client.Timeout exceeded while awaiting headers)
```

Thanks in advance for any help

Start by reviewing the reported paths in bserver_remote.go, block_retrieval_queue.go, folder_branch_ops.go, and dir.go, then reproduce or inspect the "block does not exist" handling for the affected team folder. The issue is resolved when the missing blocks are explained and a verified recovery or remediation path is established; the log-send failure is a separate diagnostic concern.

Written by the indexing model from the issue text.