ReadyNAS Ultra Plus on OS 6.10.1 becoming unresponsive

Looking at the Kernel log and System log I found no errors during the 24 hr. period prior to the time I noticed the NAS became unresponsive. I only found several kernel warning messages such as this one:

Jul 04 18:16:18 ReadyNAS6Ultra kernel: ------------[ cut here ]------------
Jul 04 18:16:18 ReadyNAS6Ultra kernel: WARNING: CPU: 0 PID: 22335 at fs/btrfs/extent-tree.c:7282 btrfs_free_extent+0x49/0xe9()
Jul 04 18:16:18 ReadyNAS6Ultra kernel: Modules linked in: nv6lcd(O) vpd(PO)
Jul 04 18:16:18 ReadyNAS6Ultra kernel: CPU: 0 PID: 22335 Comm: EmbyServer Tainted: P        W  O    4.4.178.x86_64.1 #1
Jul 04 18:16:18 ReadyNAS6Ultra kernel: Hardware name: To Be Filled By O.E.M. To Be Filled By O.E.M./To be filled by O.E.M., BIOS 080014  07/26/2010
Jul 04 18:16:18 ReadyNAS6Ultra kernel:  0000000000000000 ffff88009a0ff938 ffffffff883623e6 0000000000000000
Jul 04 18:16:18 ReadyNAS6Ultra kernel:  0000000000000009 ffff88009a0ff970 ffffffff880dbe55 ffffffff8828301e
Jul 04 18:16:18 ReadyNAS6Ultra kernel:  0000000000013907 0000000000001000 ffff88005b09fb58 ffff8800a7af4000
Jul 04 18:16:18 ReadyNAS6Ultra kernel: Call Trace:
Jul 04 18:16:18 ReadyNAS6Ultra kernel:  [<ffffffff883623e6>] dump_stack+0x4d/0x63
Jul 04 18:16:18 ReadyNAS6Ultra kernel:  [<ffffffff880dbe55>] warn_slowpath_common+0x8f/0xa8
Jul 04 18:16:18 ReadyNAS6Ultra kernel:  [<ffffffff8828301e>] ? btrfs_free_extent+0x49/0xe9
Jul 04 18:16:18 ReadyNAS6Ultra kernel:  [<ffffffff88062feb>] warn_slowpath_null+0x15/0x17
Jul 04 18:16:18 ReadyNAS6Ultra kernel:  [<ffffffff8828301e>] btrfs_free_extent+0x49/0xe9
Jul 04 18:16:18 ReadyNAS6Ultra kernel:  [<ffffffff882acc09>] __btrfs_drop_extents+0xb2e/0xc85
Jul 04 18:16:18 ReadyNAS6Ultra kernel:  [<ffffffff882d4122>] btrfs_log_changed_extents+0x2ad/0x4fb
Jul 04 18:16:18 ReadyNAS6Ultra kernel:  [<ffffffff882d4e0c>] btrfs_log_inode+0xa9c/0xc2e
Jul 04 18:16:18 ReadyNAS6Ultra kernel:  [<ffffffff8807e2be>] ? default_wake_function+0xd/0xf
Jul 04 18:16:18 ReadyNAS6Ultra kernel:  [<ffffffff8808de2f>] ? autoremove_wake_function+0xd/0x2f
Jul 04 18:16:18 ReadyNAS6Ultra kernel:  [<ffffffff882d5b68>] btrfs_log_inode_parent+0x27b/0x733
Jul 04 18:16:18 ReadyNAS6Ultra kernel:  [<ffffffff880de31a>] ? __filemap_fdatawrite_range+0xbe/0xca
Jul 04 18:16:18 ReadyNAS6Ultra kernel:  [<ffffffff88298b8d>] ? wait_current_trans.isra.9+0x1d/0xdf
Jul 04 18:16:18 ReadyNAS6Ultra kernel:  [<ffffffff88297815>] ? join_transaction.isra.3+0x20/0x3ac
Jul 04 18:16:18 ReadyNAS6Ultra kernel:  [<ffffffff882d6e58>] btrfs_log_dentry_safe+0x55/0x70
Jul 04 18:16:18 ReadyNAS6Ultra kernel:  [<ffffffff882ae961>] btrfs_sync_file+0x226/0x2da
Jul 04 18:16:18 ReadyNAS6Ultra kernel:  [<ffffffff881416d2>] vfs_fsync_range+0x86/0x95
Jul 04 18:16:18 ReadyNAS6Ultra kernel:  [<ffffffff8811d08c>] ? vfs_write+0x152/0x160
Jul 04 18:16:18 ReadyNAS6Ultra kernel:  [<ffffffff881416f8>] vfs_fsync+0x17/0x19
Jul 04 18:16:18 ReadyNAS6Ultra kernel:  [<ffffffff88141726>] do_fsync+0x2c/0x45
Jul 04 18:16:18 ReadyNAS6Ultra kernel:  [<ffffffff8814192d>] SyS_fsync+0xb/0xf
Jul 04 18:16:18 ReadyNAS6Ultra kernel:  [<ffffffff888e43ca>] entry_SYSCALL_64_fastpath+0x1e/0x8e
Jul 04 18:16:18 ReadyNAS6Ultra kernel: ---[ end trace fc8abb8082935d98 ]---

On the disk_info and SMART logs, I found no new errors either:

time			model			serial			realloc_sect	realloc_evnt	spin_retry_cnt	ioedc		cmd_timeouts	pending_sect	uncorrectable_err	ata_errors
-------------------	--------------------	--------------------	------------	------------	--------------	----------	------------	------------	-----------------	----------
2019-06-14 07:36:38	WDC WD60EFRX-68L0BN1	WD-WX41DC6A1352		0		0		0		-1		-1		0		0			0         
2019-06-14 07:36:38	WDC WD60EFRX-68L0BN1	WD-WX41DC6PFZH6		0		0		0		-1		-1		0		0			0         
2019-06-14 07:36:39	WDC WD60EFRX-68MYMN1	WD-WX81D6550PP3		0		0		0		-1		-1		0		0			0         
2019-06-14 07:36:39	HITACHI HUS724040ALE	PBG6S49S		0		0		0		-1		-1		0		0			0         
2019-06-16 12:27:36	HGST HDN724040ALE640	PK2338P4GT3WWC		0		0		0		-1		-1		0		0			103       
2019-06-18 14:25:43	HGST HDN724040ALE640	PK1334PCJAZHES		0		0		0		-1		-1		0		0			1         

One of the HGST disks shows 103 ATA errors, however this is the very initial state the disk had once it was moved into the ReadyNAS. Prior to this, the this was in a two bay NAS where it worked with no problems for a couple of years. I have been monitoring this and the error count has not increased since it was installed in the ReadyNAS array.