Decided recently to utilize aria2 with pacman.confsuch that a part of my .conf file has this in it:

XferCommand = /usr/bin/aria2c --allow-overwrite=true --continue=true --file-allocation=none --log-level=error --max-tries=2 --max-connection-per-server=2 --max-file-not-found=5 --min-split-size=5M --no-conf --remote-time=true --summary-interval=60 --timeout=5 --dir=/ --out %o %u

This is exactly as posted on the Arch Wiki: https://wiki.archlinux.org/index.php/Pacman/Tips_and_tricks#aria2

I am getting multiple lines of the following:

error: could not open file /var/lib/pacman/sync/antergos.db: Unrecognized archive format
error: could not open file /var/lib/pacman/sync/antergos.db: Unrecognized archive format

which follows from this output below: (only a smaller sample of a larger output).

aria2 will resume download if the transfer is restarted.
If there are any errors, then see the log file. See '-l' option in help/man page for details.

03/22 10:48:51 [NOTICE] Download complete: //var/lib/pacman/sync/antergos.db.part
[#561468 208KiB/271KiB(76%) CN:1 DL:252KiB]                                                                                                                                                           
03/22 10:48:52 [NOTICE] Download complete: /antergos.db

Download Results:
gid   |stat|avg speed  |path/URI
======+====+===========+=======================================================
dfbbb7|OK  |        n/a|//var/lib/pacman/sync/antergos.db.part
561468|OK  |   244KiB/s|/antergos.db

Status Legend:
(OK):download completed.

03/22 10:48:53 [ERROR] CUID#7 - Download aborted. URI=http://mirrors.antergos.com/antergos/x86_64/antergos.db.sig
Exception: [HttpSkipResponseCommand.cc:222] errorCode=3 Resource not found

03/22 10:48:53 [NOTICE] Download GID#a438faac80a5203e not complete: //var/lib/pacman/sync/antergos.db.sig.part

Download Results:
gid   |stat|avg speed  |path/URI
======+====+===========+=======================================================
a438fa|ERR |       0B/s|//var/lib/pacman/sync/antergos.db.sig.part

Status Legend:
(ERR):error occurred.

aria2 will resume download if the transfer is restarted.
If there are any errors, then see the log file. See '-l' option in help/man page for details.
[#875d22 0B/0B CN:1 DL:0B]                                                                                                                                                                            
03/22 10:49:06 [ERROR] CUID#7 - Download aborted. URI=http://downloads.sourceforge.net/project/xenlism-wildfire/repo/arch/xenlism-arch.db
Exception: [AbstractCommand.cc:334] errorCode=2 Timeout.

03/22 10:49:06 [NOTICE] Download GID#875d220385db7c26 not complete: //var/lib/pacman/sync/xenlism-arch.db.part

Download Results:
gid   |stat|avg speed  |path/URI
======+====+===========+=======================================================
875d22|ERR |       0B/s|//var/lib/pacman/sync/xenlism-arch.db.part

Status Legend:
(ERR):error occurred.

aria2 will resume download if the transfer is restarted.
If there are any errors, then see the log file. See '-l' option in help/man page for details.

As mentioned, that is when the above error occurs.

There is nothing remarkable in pacman’s log file in /var/log/pacman.log as suggested to look into
(most recent listing of transactions):

[2016-03-22 10:48] [PACMAN] Running 'pacman -Syu'
[2016-03-22 10:48] [PACMAN] synchronizing package lists
[2016-03-22 10:49] [PACMAN] starting full system upgrade
[2016-03-22 10:53] [ALPM] transaction started
[2016-03-22 10:53] [ALPM] upgraded libwbclient (4.3.6-1 -> 4.4.0-1)
[2016-03-22 10:53] [ALPM] upgraded smbclient (4.3.6-1 -> 4.4.0-1)
[2016-03-22 10:53] [ALPM] transaction completed

So as an example, using libwclient, shows nothing remarkable.

pacman -Ql libwbclient
libwbclient /usr/
libwbclient /usr/include/
libwbclient /usr/include/samba-4.0/
libwbclient /usr/include/samba-4.0/wbclient.h
libwbclient /usr/lib/
libwbclient /usr/lib/libwbclient.so
libwbclient /usr/lib/libwbclient.so.0
libwbclient /usr/lib/libwbclient.so.0.12
libwbclient /usr/lib/pkgconfig/
libwbclient /usr/lib/pkgconfig/wbclient.pc
libwbclient /usr/lib/samba/
libwbclient /usr/lib/samba/libwinbind-client-samba4.so

So as you know, in var/lib/pacman/sync/ is only listed the databases
antergos.db community.db core.db extra.db multilib.db xenlism-arch.db

How to remove or resolve error messages?
Is this normal behaviour when using arai2 with pacman?
I should state that I am using reflector. Is it safe to use aria2 in the pacman.conf while using reflector?