Trying to understand why curl calls are slow on codeigniter app - codeigniter

Question

Previous note: I'm a Windows dev, to please bear with me since this is seems to be a Linux issue.
We're having some issues with a PHP app (which was built with codeigniter, I believe). The app is hosted on Ubuntun 16.04 Server (Apache) and I think it's using PHP 7.4.
The issue: the controllers which return the html shown by the browser call a couple of web services (which are hosted on a server that is on the same network) and these call are slow (each takes amore than 1 second to complete).
We've noticed this because we installed and enabled XDebug on both servers. For our test scenario (which envolves loading 2 or 3 pages), we've ended up with the following:
The main portal log file shows that curl_exec required around 32 seconds for performing around 25 calls
The services log files shows that it only run for about 2 second (for loading and returning the data consumed by the curl calls)
Since it looked like there were some issue with the network stack, we've activated wireshark and it looks like each web service call is taking more than one second to complete (so, it seems to confirm the xdebug logs that pointed to a communication issue). For instance, here's a screenshot of one of those calls:
It seems like the ACK for the 1st application data is taking more than one second (RTT time is over 1 second). This does not happen with the following ack (for instance, 122 entry is an ack for 121 and in this case the rtt is about 0.0002 seconds). Btw, here's the info that is shown for the application data entry that is being ack after 1 second:
Frame 116: 470 bytes on wire (3760 bits), 470 bytes captured (3760 bits)
Encapsulation type: Ethernet (1)
Arrival Time: Jul 7, 2020 15:46:23.036999000 GMT Daylight Time
[Time shift for this packet: 0.000000000 seconds]
Epoch Time: 1594133183.036999000 seconds
[Time delta from previous captured frame: 0.000405000 seconds]
[Time delta from previous displayed frame: 0.000405000 seconds]
[Time since reference or first frame: 3.854565000 seconds]
Frame Number: 116
Frame Length: 470 bytes (3760 bits)
Capture Length: 470 bytes (3760 bits)
[Frame is marked: False]
[Frame is ignored: False]
[Protocols in frame: eth:ethertype:ip:tcp:tls]
[Coloring Rule Name: TCP]
[Coloring Rule String: tcp]
Ethernet II, Src: Microsof_15:5a:5e (00:15:5d:15:5a:5e), Dst: Fortinet_09:03:22 (00:09:0f:09:03:22)
Destination: Fortinet_09:03:22 (00:09:0f:09:03:22)
Address: Fortinet_09:03:22 (00:09:0f:09:03:22)
.... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
.... ...0 .... .... .... .... = IG bit: Individual address (unicast)
Source: Microsof_15:5a:5e (00:15:5d:15:5a:5e)
Address: Microsof_15:5a:5e (00:15:5d:15:5a:5e)
.... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
.... ...0 .... .... .... .... = IG bit: Individual address (unicast)
Type: IPv4 (0x0800)
Internet Protocol Version 4, Src: 10.50.100.28, Dst: 10.50.110.100
0100 .... = Version: 4
.... 0101 = Header Length: 20 bytes (5)
Differentiated Services Field: 0x00 (DSCP: CS0, ECN: Not-ECT)
0000 00.. = Differentiated Services Codepoint: Default (0)
.... ..00 = Explicit Congestion Notification: Not ECN-Capable Transport (0)
Total Length: 456
Identification: 0x459c (17820)
Flags: 0x4000, Don't fragment
0... .... .... .... = Reserved bit: Not set
.1.. .... .... .... = Don't fragment: Set
..0. .... .... .... = More fragments: Not set
...0 0000 0000 0000 = Fragment offset: 0
Time to live: 64
Protocol: TCP (6)
Header checksum: 0x0cb0 [validation disabled]
[Header checksum status: Unverified]
Source: 10.50.100.28
Destination: 10.50.110.100
Transmission Control Protocol, Src Port: 34588, Dst Port: 443, Seq: 644, Ack: 5359, Len: 404
Source Port: 34588
Destination Port: 443
[Stream index: 5]
[TCP Segment Len: 404]
Sequence number: 644 (relative sequence number)
[Next sequence number: 1048 (relative sequence number)]
Acknowledgment number: 5359 (relative ack number)
1000 .... = Header Length: 32 bytes (8)
Flags: 0x018 (PSH, ACK)
000. .... .... = Reserved: Not set
...0 .... .... = Nonce: Not set
.... 0... .... = Congestion Window Reduced (CWR): Not set
.... .0.. .... = ECN-Echo: Not set
.... ..0. .... = Urgent: Not set
.... ...1 .... = Acknowledgment: Set
.... .... 1... = Push: Set
.... .... .0.. = Reset: Not set
.... .... ..0. = Syn: Not set
.... .... ...0 = Fin: Not set
[TCP Flags: ·······AP···]
Window size value: 319
[Calculated window size: 40832]
[Window size scaling factor: 128]
Checksum: 0x8850 [unverified]
[Checksum Status: Unverified]
Urgent pointer: 0
Options: (12 bytes), No-Operation (NOP), No-Operation (NOP), Timestamps
TCP Option - No-Operation (NOP)
Kind: No-Operation (1)
TCP Option - No-Operation (NOP)
Kind: No-Operation (1)
TCP Option - Timestamps: TSval 1446266633, TSecr 1807771224
Kind: Time Stamp Option (8)
Length: 10
Timestamp value: 1446266633
Timestamp echo reply: 1807771224
[SEQ/ACK analysis]
[This is an ACK to the segment in frame: 115]
[The RTT to ACK the segment was: 0.000405000 seconds]
[iRTT: 0.000474000 seconds]
[Bytes in flight: 404]
[Bytes sent since last PSH flag: 404]
[Timestamps]
[Time since first frame in this TCP stream: 0.010560000 seconds]
[Time since previous frame in this TCP stream: 0.000405000 seconds]
TCP payload (404 bytes)
Transport Layer Security
TLSv1.2 Record Layer: Application Data Protocol: http-over-tls
Content Type: Application Data (23)
Version: TLS 1.2 (0x0303)
Length: 399
Encrypted Application Data: 6611c266b7d32e17367b99607d0a0607f61149d15bcb135d…
Any tips on what's going on?
Thanks.