There are other 2.4GHz wireless signals in the area. Even setting the
channel HT mode to 20MHz only and changing the wireless channel did not
fix the issue. The issue was resolved when “Aggregation” was
disabled on the Wireless Advance Settings.

Additional Notes about aggregation:

Aggregation significantly increases the efficiency of the WM.
Throughput on a WM with aggregation enabled is far higher. 802.11ac has
now made this form of aggregation mandatory so WM will become much more
efficient. This will make WLANs much more reliable.

Figure 1. A Normal 802.11 exchange (LEFT) A A-MPDU exchange
(RIGHT)

Wireless may have started out unreliable, slow, and unsecure, but it has
come a long way since then. Now there are new standards that boast up to
7Gbps and new protocols to make wireless not only reliable, but able to
use the WM effectively. The technologies listed above are the significant
enhancements in 802.11, but there are many more that also help the WM
become dependable.