The PSE (Power Sourcing Equipment) allocates a slightly less value (difference up to ~0.5w) between the PD (Powered Device) requested power values and PSE allocated power values.

To identify the issue execute the CLI command:
user@device> show lldp neighbors interface <interface>
user@device> show poe interface <interface>

Example of the issue:

AP requests 25.5 watts, however switch provides 25.4 only

AP requests 19.5 watts, however switch provides only 19.3w

root@switch> show poe interface mge-2/0/4

PoE interface status:

PoE interface : mge-2/0/4

Administrative status : Enabled

Operational status : ON

Operational status detail : 4P Port delivering 2P IEEE SSPD

FourPair status : Disabled

Power limit on the interface : 19.3W (L)

Priority : Low

Power consumed : 6.4W

Class of power device : 4/-

PoE Mode : 802.3bt

(L) LLDP-negotiated value on the port.

root@switch> show poe interface mge-2/0/7

PoE interface status:

PoE interface : mge-2/0/7

Administrative status : Enabled

Operational status : ON

Operational status detail : 4P Port delivering 4P IEEE SSPD

FourPair status : Disabled

Power limit on the interface : 25.3W (L)

Priority : Low

Power consumed : 11.0W

Class of power device : 6/-

PoE Mode : 802.3bt

(L) LLDP-negotiated value on the port.

This software problem was reported and solved on https://prsearch.juniper.net/problemreport/PR1716261